A Source Book in Medieval Science

Author: Pierre d'Ailly  | Date: 1930

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The Image or Representation of the World (Ymago Mundi)

Pierre d’Ailly, with the Marginal Comments of Christopher Columbus

Translated and annotated by Edward Grant1

The image of the world, or imaginary description of it representing it as in a physical mirror,2 is not without use for the elucidation of Holy Scriptures, which frequently make mention of its parts and especially about the places of the habitable earth. It is because of this that I was led to write this treatise and thought it worthwhile to have gathered, briefly and truthfully, things that have been written diffusely by scholars on this subject.


The treatise is divided into sixty chapters.

1.3 The first chapter treats generally of the world and its parts.

2. On circles and other parts that are imagined in the sky.

3. On the path of the sun and its year and days.

4. On the four elements and their location.

5. On the size (quantitate) of the earth and its measurement.

6. On the division of the whole earth.

7. On the variety of opinions concerning the habitation of the earth.

8. On the size (quantitate) of the habitable earth.

9. On the division of the habitable earth into climes (climata) by the astronomers.

10. On the longitude and latitude of the climes.

11. On the anteclimes and postclimes.

12. On the uninhabitable places.

13. On a difference between habitable places.

14. On the division of the earth into three parts according to the cosmographers.

15. On the parts of Asia, taking India first.

16. On the wonders of India.

17. On the parts of Asia after India, taking Parthia (Persia) first.

18. On Mesopotamia and its regions.

19. On Syria and its provinces.

20. On the size of the Promised Land (terre promissionis).

21. On Egypt.

22. On the regions adjacent to Egypt according to Orosius.

23. On the aforesaid regions according to Isidore.

24. On certain kingdoms of the aforesaid regions.

25. On Asia Minor and its provinces.

26. On Europe, taking the barbaric part first.

27. On the provinces which the Danube separates from the barbaric part.

28. On Greece and its provinces.

29. On Italy and its provinces.

30. On Gaul and its provinces.

31. On Spain and its parts.

32. On Africa in general.

33. On the provinces of Africa, taking Cyrenaica first.

34. On Tripolitania and Byzantium.

35. On Carthage and Numidia.

36. On Mauretania and its parts.

37. On Ethiopia and its parts.

38. On famous mountains.

39. On famous promontories.

40. On the western islands of the ocean.

41. On other well-known islands of the ocean.

42. On the island of Taprobane, especially of India.

43. On the islands of the Mediterranean Sea, taking Cyprus first.

44. On the Cyclades islands.

45. On Sicily and its neighboring islands.

46. On Sardinia and Corsica.

47. On the islands of Massilia and Spain.

48. On smaller and less well-known islands.

49. On the types of waters, taking the ocean first.

50. On the Mediterranean Sea.

51. On gulfs of the sea and especially of the Red Sea.

52. On tides (estibus) and straits (fretis) of a sea.

53. On lakes and standing waters, taking the Dead Sea first.

54. On other principal lakes and standing waters, taking the Caspian Sea first.

55. On rivers; the Nile first.

56. On the rivers of Paradise.

57. On other rivers of Asia.

58. On the Jordan river especially.

59. On the rivers of Europe and Africa.

60. On winds and the difference between them.



The world has a spherical4 or round figure with a variety of many parts. First, it is composed of four elements: earth, water, air, and fire. Then [it is composed] of nine heavens [or spheres] (ex nonem celis), namely of the heaven of the Moon (ex celo Lune), Mercury, Venus, the Sun, Mars, Jupiter, Saturn, the firmament, and the first mobile.5 Beyond this certain philosophers assume a tenth immobile heaven; and beyond this there is said to exist a crystalline heaven [or sphere] and then comes the empyrean heaven [or sphere], the outermost of all [spheres], where the abode of God is and the dwelling of the saints.6 But, speaking naturally, [that is, in terms of natural phenomena alone] these last two do not fall within the scope of philosophers and astronomers. Few astronomers concern themselves with the tenth immobile heaven, but are rather concerned in their speculations with the other nine. In the first place, they assume that the ninth sphere, or first mobile [the sphere that is moved first], exists where there are no stars and that its motion is regular and uniform, moving around the whole earth in a natural day and carrying with it all the other spheres from east to west. After this heaven [or sphere] is the eighth sphere, which is called the firmament, that is, the starry sky, whose proper and natural motion is contrary to that of the first mobile and all the other spheres, namely from west to east. But it does not move [from west to east] absolutely, but moves in a contrary way with a certain declination. According to Ptolemy, this motion of the firmament is 1 degree in one hundred years made around the poles of the zodiac; and according to Thabit [ibn Qurra, this degree is acquired] on the first points of Aries and Libra. Thus its complete revolution is made in 36,000 years, which is called a Great Year.7 Then come the seven spheres of the planets named above, which complete their revolutions in different times with a proper motion from west to east, as Saturn in around thirty years, Jupiter in almost twelve years, Mars in around two years, the sun, Mercury, and Venus in one year, and the moon in 27 days and 8 hours.8

Of the aforementioned spheres, astronomers have been chiefly concerned with the eighth sphere because its influence is powerful and strong, and in it, or under it, are found all the stars. Ancient wise men assumed that there were 1029 principal stars, namely the seven planets, which are called wanderers because their motions are diverse and on different circles, and 1022 fixed stars. . . .9

. . . . . . .



After treating to some extent of the heaven, we must now consider the things that lie under it.

Immediately after [or below] the sphere of the moon, the philosophers place the sphere of fire, which is most pure there and invisible because of its rarity. Just as water is clearer than earth and air than water, so this fire is rarer and clearer than air, and so is the heaven [or sky] rarer or clearer than fire, except for the stars, which are thicker [or denser] parts of the sky so that the stars are lucid and visible. Afterwards is the sphere of air, which encloses water and earth. This is divided into three regions, one of which is the outermost (next to fire) where there is no wind, rain, or thunder, nor any phenomenon of this kind, and where certain mountains, such as Olympus, are said to reach. Aristotle says11 that starry comets appear and are made there and that the sphere of fire and this supreme region of air with its comets are moved simultaneously with the heaven [or sky] from east to west.12 The middle region [of air], however, is where the clouds are and where various phenomena occur,13 since it is always cold. The other [and third] region is the lowest, where the birds and beasts dwell.14 Then follow water and earth, for water does not surround the whole earth, but it leaves a part of it uncovered for the habitation of animals. Since one part of the earth is less heavy and weighty than another, it is, therefore, higher and more elevated from the center of the world. The remainder [of the earth], except for islands, is wholly covered by waters according to the common opinion of philosophers.15 Therefore, the earth, as the heaviest element, is in the center or middle of the world, so that the earth’s center is the center of its gravity; or, according to some, the center of gravity of the earth and also of water is the center of the world.16 And although there are mountains and valleys on the earth, for which reason it is not perfectly round, it approximates very nearly to roundness. Thus it is that an eclipse of the moon, which is caused by the shadow of the earth,17 appears round. They say the earth is round, therefore, because it approximates to roundness.



Having assumed the roundness of the earth, one must presuppose for the measurement of its size that in going from one side of the earth to the other, one part of the sky after another will appear and that the horizon varies. If anyone should go from the north directly toward the south, the north pole would appear to him continually less elevated; and if he went the other way, it would appear to him more elevated. And if he should go directly southward along one meridian such that the north pole were less elevated on the horizon by a twelfth part of the meridian, [then] he would have traversed a twelfth part of the earth’s circuit; and if he went so that the pole appeared less elevated to him by 1 degree, he would then have traversed 1 degree of the earth’s circuit, and there are 360 such parts in its circuit. It is by this method that the measure of the earth was found, because the elevation of one pole or one star is easily found by means of an astrolabe or quadrant,18 Now, it is found by experience that if one goes toward the north so that the pole is more elevated by 1 degree, or directly toward the south so that it is less elevated by 1 degree, he will have traversed 700 stades of the earth. And according to the author of the Sphere, it is necessary to multiply this number by 360, so that we shall have 252,000 stades for the whole circuit [or circumference] of the earth,19 which equals 15,750 leagues, since 1 league equals 2 miles, and 1 mile equals 8 stades; 1 stade equals 125 paces;20 1 pace equals 5 feet; 1 foot, 4 palms; and 1 palm, 4 digits. It is obvious, then, that if one traveled 10 leagues per day, he could go round the earth in 1570 days, which equals 4 years, 16 weeks, and 2 days.21

Knowing the size of the earth’s circumference, there is a given rule by which the size of its diameter can be known: subtract from the circle its twenty-second part and divide the remainder into three parts and the diameter equals one of these thirds. And so it is that the diameter equals 80,181 stades plus 1/2 and 1/3 of a stade,22 which equals 2505 leagues plus 1/2 and 3 stades. Knowledge of this, although not completely precise, is, however, wonderful and useful, since it has no notable deficiency23 and especially since Ptolemy and other wisemen have shown the size of the stellar bodies by means of the size of the earth; and by the size of the earth’s radius (dimidii dyametri) they have shown the distance of the stars from the pole of the earth (cuspide terre).24 But it is not our present intention to describe these quantities. It is sufficient here to note that the sun is much greater than any other star and that some say that the magnitude [or size] of its body is equal to more than 166 times that of the earth,25 although some say, as does Isidore, that it is only 8 times greater than the earth.26 After the sun, there come [in order of size] the greatest of the fixed stars, namely those in the first magnitude of stars, after which Jupiter is the greatest, then Saturn. The rest of the fixed stars follow in order of their degrees [of magnitude] until we reach the stars in the sixth magnitude; then come Mars, Venus, the Moon, and finally, Mercury.27 Each of these stars is perceptibly larger than the earth, except for the last three, which are smaller than it.28 This is obvious, because among all the stars perceptible to the sight, these three are smallest, since all the others are said to be greater than the whole earth. Any one of the stars in the first magnitude is approximately equal to 107 times the size of the earth; and any one of the stars in the sixth magnitude is [approximately] equal to 18 times the size of the earth.29 From all this, it is also obvious that the philosophers say with good reason that the size of the earth is as a point in relation to the size of the heaven [or sky].30



The earth is divided proportionally, just as the sky is divided into four quarters, by two colures and the equinoctial [circle or celestial equator];32

and these circles on the earth are similarly divided by degrees and minutes, so that the whole circumference is 360 degrees and a fourth part is 90 degrees. Just as the sky, the earth is divided proportionally by four smaller circles into five unequal parts, namely by two circles, arctic and antarctic, and by two tropics. And the five zones on earth are said to be [related] proportionally just as [the zones] in the sky, because certain districts or regions on earth correspond to those zones. The first zone is located between the arctic pole and arctic circle;33 the second between the arctic circle and summer tropic; the third between the summer tropic and winter tropic; the fourth between the winter tropic and antarctic circle; the fifth between the antarctic circle and antarctic pole.34 Furthermore, the distance of these zones is unequal, because the distance of the pole of the zodiac [that is, the pole of the ecliptic] from the pole of the world [that is, the pole of the celestial equator] is 23 degrees, 51 minutes.35 The maximum declination of the sun is the same as the distance between the pole of the zodiac and the pole of the world. Indeed, the arc cut off between the maximum declination of the sun and pole of the zodiac is 42 degrees, and 18 minutes.36

According to some, the first and last of these zones or regions of the earth are uninhabitable because of excessive cold, since they are so far from the sun.37 The third zone, which is the middle zone, lies under the sun’s path and is very near it; and therefore it is called the torrid zone and is said to be uninhabitable because of excessive heat.38 The other two, namely the second and fourth, are neither excessively close nor far from the sun and so are temperate in heat and cold, and from this standpoint they are habitable unless something else should hinder them. In this division of the earth, I called that which is in the direction of the arctic pole, which always appears to us, the first zone, even though Aristotle, in assigning the differences of position in the sky says that the antarctic pole is the top of the world;39 from this standpoint we are at the bottom and left side of the world because we dwell toward the west and the arctic [or north] pole. But if we consider the proper motion according to the zodiac, which is carried along in a contrary motion, as has been said, then the arctic [or north] pole is above, because this motion is perhaps more noble, and the spheres which are so moved are more noble, and the greater multitude of noble stars is in this half of the sky towards the arctic pole, at least with regard to the half [of the sky] that appears visible to us. In accordance with this, we should be in the superior and nobler part and to the right. Thus the first zone should be towards the arctic pole.40

. . . . . . .



In order to investigate the size of the habitable part of the earth, it must be understood that "habitable" is taken in two ways. In one way it is taken with regard to the sky, namely how much can, and how much cannot, be inhabited because of the sun.41 This was discussed above in general and enough was said. In the other way, "habitable" is considered with respect to water, namely as water limits [or prevents] habitability;42 and we must now consider this on which wise men offer various opinions.

For Ptolemy, in his book On the Arrangement of the Sphere (De dispositione sphere)43 would have it that about a sixth part of the earth is habitable because [of an absence] of water and all the rest is covered by water. But in his Almagest, Book II, he posits the known habitation extends over only one fourth of the earth, namely over the part on which we dwell, which extends in longitude from east to west, embracing half of the equinoctial circle [that is, equator], and the whole latitude extends from the equator to the [north] pole, covering one fourth of the colure.44

But at the end of his book On the Heavens and World, Aristotle says that it covers more than one fourth, and Averroes confirms this.45 Aristotle says that a small sea lies between the end of the western side of Spain and the beginning of the eastern part of India.46 But he was not speaking of Hither Spain, which is now commonly called Spain, but [rather] of Farther Spain, which is now called Africa [and] of which certain authors, as Pliny, Orosius, and Isidore have spoken.47 Moreover, Seneca, in the fifth book of Natural Things [that is, The Natural Questions] says that if the wind is favorable, this sea is navigable in a few days. And Pliny, in the second book of the Natural History, teaches that some have navigated from the Arabian Gulf to the Pillars of Hercules [that is, Straits of Gibralter] in a time that is not very great.48 For these and other reasons, which I shall consider further when I speak of the ocean, some conclude, apparently, that the sea is not so great that it could cover three fourths of the earth. To this can be added the authority of Esdras, who in his fourth book says that six parts of the earth are inhabited and the seventh is covered by water.49 The saints hold in reverence the authority of this book and the sacred truths confirmed by it. And so it seems that although the inhabited part known to Ptolemy and his followers was confined below one fourth, more than that is habitable.50 But

Aristotle, with the aid of Alexander, was able to know more about this, as was Seneca, with the aid of Nero; for they had been stimulated to investigate doubtful things about this world. Pliny, in his eighth book,51 and Solinus52 also testify about Alexander; and Seneca tells about Nero in his book on Natural Things.53 It seems that they ought more to be believed than Ptolemy or even Albategni [al-Battani], who assumes that even less of the earth is habitable, namely only a twelfth part;54 but this lacks proof, as could be shown, but by reason of brevity I pass over this, because even from what follows this will be obvious.

Thus, from what has already been said and what will be said below, it appears that the habitable earth is not round as a circle, as Aristotle says, but is as the fourth part of the surface of a sphere, of which fourth the two extreme parts are somewhat cut off, namely those which are not habitable because of excessive heat or cold. But this cannot be as suitably figured on a plane [map] as on a spherical [one].55

. . . . . . .



Every clime has more longitude than latitude, because longitude proceeds from east to west and latitude from the south toward the north. According to astronomers, the first clime contains in longitude half the circumference of the earth, which some measure by stades, as was said above. But Alfraganus and certain others measure it by miles57 and say that any degree of the earth’s circumference contains

miles,58 so that the whole circumference contains 20,400 miles and half would be 10,200 miles, which, if 1 league is reckoned as 2 miles, equals 5100 leagues, the length of the first clime. The second clime would be shorter than the first and the third less than the second, and so on, in ascending northward. But authors do not assume certitude for the measure of longitude of these climes. The longitude [or length] of these climes has been found by the aspect at [the time] of eclipse of the moon.

The latitude [or width] of these climes is measured from south to north. The beginning of the first clime is 12 degrees and some minutes this side of the equator, which according to Alfraganus, is equivalent to

miles, which equals
leagues. . . .



From what has been said, the climes when taken together are terminated by two lines, one of which begins the first clime and is

degrees from the equator,59 the other terminates the seventh clime. Some designate as "anteclimes" areas inhabited beyond the first line and as "postclimes" those areas beyond the second line. Now, it has been proven by experience and the authority of many that not only are the seven climes inhabited, but more than one fourth of the earth contains nations of men, so that authors assume more inhabited areas beyond [or below] the first line.60 According to Pliny, in the second, fifth, and sixth books,61 and Ambrose in the fourth book of his Hexameron,62 there are, in parts of the south, some who are without shade for two days of the year because they have the sun over their heads and are illuminated everywhere by its revolution. For this reason they are called "Ascii",63 that is, without shade, and "Amphiscii,64 that is, surrounded by shadows. And these people are below the equator and, according to Pliny,65 are called "Orestes," "Menodes," and "Symarians." Located among them is a mountain named Malk on which the shadows are changed every six months. And yet beyond the equator, Haly places two cities,66 one of which is called Deleyt, whose longitude is 122 degrees and whose latitude is 3 degrees; and the other is called Baraya, whose longitude is 125 degrees and whose latitude 3 degrees. Moreover, according to Pliny, we find that there is habitation under the tropic of Capricorn and beyond. Thus there is a region called the island of Pathalis possessing a famous port where shadows fall only to the south. Therefore, those who dwell in this place have the sun always to the north.67 And in the sixth book [of his Natural History, Pliny] says68 the same thing about the island of Taprobane [Ceylon], whose inhabitants who came to Rome during the principate of Claudius were amazed that their shadows fell to the north and that they rose to the south.69 According to Albategni, this island is opposite India toward the east. . . .70

As for the line which terminates the climes toward the north, there is much inhabited [land] beyond it, as England, Scotland, Dacia, Norway, and several other regions, the last of which, according to some, is the island of Thule.

And according to Aristotle and Averroes at the end of the second book of De caelo et mundo, the end of the habitable earth toward the east and the end of the habitable earth toward the west are very close and there is a small sea between;71 but its latitude over the earth extends over a distance greater than half the circumference of the earth. Thus, if, as some authors say, the climes are extended to the western extremity but do not extend in length beyond half the circumference of the earth, it follows, according to Averroes, that the climes do not extend to the eastern extremity but that there are large inhabited areas beyond, namely beyond the climes toward the east. It is necessary, therefore, that the climes, or some of them, be longer than the astronomers suppose.72 And this briefly is what I want to say about those places which are beyond the climes.73

1. Pierre d’Ailly completed the Ymago Mundi on August 12, 1410, and it was printed at Louvain between 1480 and 1483 in a volume containing fifteen other treatises by d’Ailly and five by Jean Gerson. A copy of this volume was subsequently annotated in Latin by Columbus before his first voyage of discovery (this volume is today preserved in Seville). Although most of the annotations are mere repetitions of d’Ailly’s text, they will be translated here, so that the reader can see not only what Columbus deemed worthy of emphasis but also something of his views about world geography and thereby acquire a sense of the background to Columbus’ historic voyages. It is noteworthy that of the books which Columbus read and annotated between 1485 and 1490, the Ymago Mundi was one of the most important. Indeed, it "seems to have been Christopher’s bedside book for a number of years . . ." (Samuel Eliot Morison, Admiral of the Ocean Sea [Boston: Little, Brown, 1942], I, 120). These annotations will be presented as notes rather than in the margins, where Columbus wrote them.

The translation has been made from the Latin text in Vol. I of the edition by Edmond Buron, Ymago Mundi de Pierre d’Ailly (Paris: Maisonneuve Frères, 1930), which is accompanied by a facing French translation. Buron’s notes have been extremely helpful in identifying d’Ailly’s sources.

2. Many authors before d’Ailly had compared descriptions of the world to an image in a mirror, signifying by this that while the descriptions are not physically real, they can be taken to provide a perfect representation of reality.

The traditional and encyclopedic character of this treatise is nicely characterized by Buron (I, 152, n. 3; the translation is mine): "The beginning of this treatise is well known to all who have frequented the ancients even slightly. We do not venture to name any writers before d’Ailly who describe the world in the same manner as he did; for it would be necessary to enumerate some hundreds of Greek, Arabic, and Latin authors. What Isidore of Seville wrote had been said by twenty authors; what the Venerable Bede, or Honorius of Autun, or Sacro-bosco, or Albert the Great, or Michael Scot, or Vincent of Beauvais, or Bacon has compiled has served for d’Ailly and all have reproduced Isidore, or Pliny, or Solinus, or Ambrose, or Jerome, or Macrobius, or Capella, or Aristotle, Ptolemy, Strabo, Hegesippus, etc. How can one recognize the contribution of each in these encyclopedic accumulations? Some idea, or even some textual phrase, of d’Ailly is found simultaneously in Pliny, Solinus, Josephus, Isidore, Bacon, Vincent, etc. Did our author borrow his phrase from Solinus or Isidore? We can only know this if d’Ailly, or some witness, informs us of it. In the present case, this is fortunately what happens. Our author does not confide all his secrets to us, although one must recognize in him much honesty and candor; but sometimes we can disclose his neglect by analysis, by comparison of texts, by fortunate errors committed by medieval translators or editors." It may be added that sometimes d’Ailly was an unscrupulous plagiarist (see n. 10).

3. I have altered the ordinal numbers of the Latin text to cardinal numbers.

4. In the margin Columbus writes: [5] "A sphere is called a space, thus ’sphere of a sphere’ (spera spere), that is, a rotundity or body round on every side. And a sphere is [formed] when a semicircle is moved completely around a diameter that remains [at rest]; and a sphere is called a round space, and therefore the roundness of the world is called the sphere of the world because its spheres have been formed in the round. And everything round and of a round form is called a sphere because of its round form and roundness, just as the balls with which children play. ’Sphere’ comes from the Greek, for the Greeks call something that is round a sphere from whence is derived spericus, sperica, spericum, that is round and solid like a sphere. And they say that the sphere of the sky is a certain kind formed in roundness whose center is the earth enclosed equally on all sides. This sphere is turned from east and west once in a day and night with such a swiftness that if the stars did not move against [or contrary to] its swift course and retard it, it would destroy the world. They [also] say that the sphere has neither beginning nor end. And thus it is not easy to understand where what is round,as a circle, begins and ends." [The next few words are incomprehensible, followed by a few lines of little interest, which are omitted.]

The number "[5]" preceding Columbus’ comment signifies that this is his fifth marginal comment. All the comments, in this and other volumes annotated by Columbus, have been assigned numbers in order of occurrence. These will be repeated here before each comment. It should be noted that comment [5] is meant to apply to much of the material in this paragraph. Most of Columbus’ marginal notes merely repeat phrases or sentences from the text of d’Ailly.

5. The sixty chapters of the Ymago Mundi are preceded by a lengthy preface containing diagrams and tables which are relevant to various chapters. A figure (not reproduced here) showing nine concentric spheres is presented as relevant to this first chapter. In his description of the planets and spheres in this diagram, d’Ailly seems to draw upon Nicole Oresme’s Traitié de l’espere (edited by Laura McCarthy in a master’s thesis, University of Toronto, 1942), a treatise written in Old French and on which d’Ailly relied heavily in the Ymago Mundi(see n. 10). Since Oresme incorporated cosmological opinions of Aristotle, these are also reflected in the following description (Latin text in Buron, I, 126, 128):

"This figure is relevant to the first chapter. Only the nine celestial spheres which conform to the opinions of astronomers are described here; for Aristotle assumes only eight [spheres].

"Saturn is naturally cold and dry in its effect [on other things]; it is pale and of an evil disposition. Jupiter is hot and wet, clear and pure, thus tempering the maliciousness of Saturn. Mars is hot and dry, fiery and radiant, thereby harmful and provoking to war. The Sun is hot and luminous, distinguishing the times [and seasons], illuminating the stars, and greater than any [star]. Venus is hot and wet, most splendid amongst the stars, and always companion to the sun, called Lucifer when it precedes the sun [it is then a morning star—Ed.] and Vesper when it follows the sun [it would now be an evening star—Ed.] Mercury is radiant and keeps pace with the sun, being never more distant than 24 degrees. Thus it is rarely perceptible. The moon is cold and wet and the mother of waters; illuminated by the sun, it illuminates the night.

"The heaven [or sky] is not of the nature of the four elements, nor does it have any of their qualities, since it is not generable or corruptible; nor is it called hot except virtually (virtualiter), since by its power (virtute), it makes [things] hot. Nor is it properly colored, for it is clear [and lucid]; nor is it properly light or heavy; soft or hard; rare or dense. Only improperly is it called hard because it is unbreakable and impenetrable; and only improperly is it called dense or thick because a star is said to be the densest part of its sphere. Nor can it be moved slower or quicker than it is moved. Moreover, the spheres of the sky are unequal in width, not proportionally according to their magnitude, however, but [rather] according as the stars or planets [embedded] in them are greater or smaller."

Some of the special properties that were conferred upon the celestial region from Greek antiquity to the seventeenth century are described here by d’Ailly. It should be noted that in his fixed order of the planets, Venus and Mercury are placed below the sun, an order which agrees with Ptolemy (Almagest, Bk. IX, ch. 1) and Cicero (Republic, Bk. VI). See Selection 4, Macrobius.

6. Sacrobosco (On the Sphere, ch. I) lists the same nine spheres (see Selection 64.1) but ignores the tenth, the crystalline, and the empyrean heavens. By way of contrast to the view that located God at the empyrean heaven, see the cosmological discussions in Selections 72 and 73, where it is assumed that He is everywhere inside the cosmos as well as beyond in an infinite void space.

7. That is,

On the Great Year, see Selection 51.2, n. 86, and Selection 69, n. 7.

8. The periods of the planets are probably derived from Sacrobosco, On the Sphere, chapter 1; see Selection 64.1.

9. The total of 1022 fixed stars derives ultimately from Ptolemy’s Almagest, Book VIII. Since it was repeated frequently, d’Ailly could have derived it from many possible sources.

10. Although inverting the order and introducing some slight modifications, d’Ailly took this chapter from Nicole Oresme’s Traitié de l’espere (Treatise On the Sphere), chapter 1. In his Tractatus de legibus et sectis contra supersticios astronomos (Treatise on the Laws and Sects against the Superstitious Astronomers), which is the third treatise in Columbus’ edition of the Ymago Mundi, and one which he annotated, d’Ailly plagiarized much of Part III of Oresme’s On the Commensurability or Incommensurability of the Celestial Motions, part of which is included in Selection 69.

11.Meteorologica I.7.344a.9–23.

12. Columbus: [8]"Mount Olympus, where comets are made."

13. Columbus: [8]"Where phenomena occur."

14. Columbus: [8]"Where the birds dwell."

15. Columbus: [8]"Water and earth together make a round body."

16. Columbus: [9]"The center of gravity of the earth and water together is the center of the world."

17. Columbus: [9]"An eclipse of the moon is caused by the shadow of the earth."

18. Columbus: [10]"The measure of the earth was found by this method."

19. Sacrobosco, On the Sphere, chapter 1 ("Measuring the Earth’s Circumference"). See Selection 64.1. This estimate is derived ultimately from Eratosthenes (third century B.C.), who first arrived at a figure of 250,000 stades, which he subsequently altered to 252,000, probably because I degree would then be equal to 700 stades, a round number. The section from Cleomedes, On the Orbits of the Heavenly Bodies, Book I, chapter 10, which describes the methods of Posidonius and Eratosthenes in determining the measurement of the earth’s circumference, appears in M. R. Cohen and I. E. Drabkin, A Source Book in Greek Science (Cambridge, Mass.: Harvard University Press, 1948), pp. 149–153. It should be apparent that Columbus did not discover the rotundity of the earth. Aside from a few trivial exceptions, Aristotle, Ptolemy, and almost all educated men in Greek and Roman antiquity and the Middle Ages believed in its sphericity.

20. The value of the stade, in terms of feet, varied according to the different foot measurements employed (see Cohen and Drabkin, p. 150, n. 2).

21. This should be 4 years, 15 weeks, and 4 days.

22. That is,

stades, the very figure given by Sacrobosco in chapter 1 of On the Sphere (see Selection 64.1). Using d’Ailly’s figures, where π is equivalent to
the calculations yield

23. Up to this point chapter 5 is, for the most part, a translation from French into Latin of chapter 26 of Oresme’s Traitié de l’espere. Oresme had drawn some of his data from Sacrobosco’s On the Sphere.

24. Columbus:[11) "They have shown the size (quanti-tatem) of the celestial bodies by the size (quantitatem) of the earth. By the size of the earth’s radius they have shown the distance of the stars."

25. Probably derived from Roger Bacon’s Opus maius, Part IV, where Bacon records that Thabit ibn Qurra "says that the sun is equal to the earth one hundred and sixtysix times." See Robert B. Burke’s translation The Opus Majus of Roger Bacon (1928; New York: Russell and Russell, 1962), I, 256.

26. I failed to locate this reference in Isidore’s Etymologies or On the Nature of Things, but the 8 to 1 ratio of sizes between sun and earth was given, perhaps for the first time, by Macrobius in his Commentary on the Dream of Scipio, Book I, chapter 20, [32]. In his translation of Macrobius’ Commentary (New York: Columbia University Press, 1952), William H. Stahl observes that this estimate of the sun’s size was widely adopted in the Middle Ages and cites ks instances Helpericus of Auxerre (De computo XX) and Honorius of Autun (De philosophia mundi II. xxxii).

27. This particular order of the sizes of the celestial bodies was probably derived from Roger Bacon’s Opus maius, Part IV ("The Usefulness of Mathematics in Divine Things"). It is identical with Bacon’s arrangement except that between Mars and Earth, Bacon includes, and d’Ailly omits, all fixed stars that are perceptible to the sight but smaller than any in the first six magnitudes. Of these Bacon writes: "Then there are other stars in infinite number, the size of which cannot be ascertained by instruments and yet they are known by sight, and therefore have sensible size with respect to the heavens, like the part with respect to the whole" (Burke, I, 258).

28. That is, Venus, the Moon, and Mercury.

29. These size relations are identical with those given by Roger Bacon, Opus maius, Part IV (Burke I, 258).

30. Columbus: [12] "The size of the earth is as a point in relation to the size of the heaven [or sky]." D’Ailly probably took this from Sacrobosco, On the Sphere, chapter 1, where we are told that "the earth is as a center and point with respect to the firmament . . ." (see Selection 64.1). Ultimately it is traceable to Ptolemy’s Almagest, Book I, chapter 6 ("That the Earth has the Ratio of a Point to the Heavens").

31. The bulk of this chapter is drawn from Oresme’s Traitié de l’espere.

32. Columbus: [13]"The earth is divided in the same manner as the sky." The colures are two great circles intersecting at right angles at the poles; one great circle passes through the equinoctial points (that is, the points of intersection between the ecliptic and celestial equator) and the other through the solstitial points. The effect of this intersection is to divide the sky into four quarters.

33. Columbus: [14]"There are five zones on the earth, as in the sky."

34. In order, the zones are (1) the North Frigid Zone; (2) North Temperate Zone; (3) Torrid Zone; (4) South Temperate Zone; (5) South Frigid Zone. This discussion of the five climatic zones is a great improvement over that given by Isidore of Seville in his Etymologies, chapter 44, and in chapter 10 of his On the Nature of Things (see Selection 1 and note 60 thereto). In his preface d’Ailly includes a diagram to illustrate the five zones.

35. Columbus: [15] "The distance between the pole of the zodiac and the pole of the world is 23 degrees, 51 minutes." This is a value for the obliquity of the ecliptic —that is, the angle formed by the intersection of the poles of the ecliptic and celestial equator—which causes both the change of seasons and inequality of the five climatic zones previously described. Since the value for the obliquity of the ecliptic is approximately

degrees (more precisely 23 degrees, 27 minutes; the value given by d’Ailly is 23 degrees, 51 minutes; see Sacrobosco On the Sphere, ch. 2, p. 447), the frigid zones lie within
degrees of their respective poles (that is, between 90 degrees N and S latitudes and degrees
N and S latitudes, respectively); the temperate zones lie within degrees
N and S latitudes and
degrees N and S latitudes, respectively, so that each temperate zone extends over an arc of the earth’s circumference subtended by an angle of approximately 43 degrees; finally, the torrid zone, extending from the tropic of Cancer, which is
degrees N latitude, to the tropic of Capricorn, which is
degrees S latitude, embraces 47 degrees of latitude.

36. Columbus: [15]"From the tropic of Cancer to the arctic circle there are 42 degrees, 18 minutes." Using 23 degrees, 51 minutes, d’Ailly’s figure for the obliquity of the ecliptic, and observing that 23 degrees, 51 minutes, would be the extent of the North Frigid Zone and 23 degrees, 51 minutes, the angle subtending the arcal distance between equator and tropic of Cancer, we would, upon adding these two figures, obtain 47 degrees, 42 minutes. Subtracting this from 90 degrees, we get 42 degrees, 18 minutes, the angle subtending that portion of the earth’s circumference falling in the temperate zone, or the angular distance between the arctic circle and the tropic of Cancer.

37. Columbus: [15] "The Frigid Zones." For emphasis, Columbus enclosed this remark in a rectangular box.

38. Columbus: [16]"The Torrid Zone is not uninhabitable (non est inhabitabilis), because today the Portuguese navigate through it; indeed it is very populated. Below the equator there is the fort of Mine belonging to the Most Serene King of Portugal and which we have seen." Perhaps in order to emphasize his disagreement with d’Ailly and traditional accounts of the uninhabit-ability of the torrid zone, Columbus drew a rectangular box around this marginal comment. Apparently oblivious to his opinion here, d’Ailly remarks later on that experience shows that the region below the first clime is inhabited. See beginning of chapter 1 and note 60, where Columbus notes d’Ailly’s opinion without drawing attention to the conflicting judgment given here.

39. Columbus: [16]"Aristotle. The antarctic pole is at the top of the world." Aristotle argued that the celestial sphere had a top and bottom and a right and left. The celestial pole furnished top and bottom, and in a seemingly strange argument, Aristotle insisted that the north (or visible) pole is the bottom and the south (or invisible or antarctic) pole the top. "Clearly therefore the invisible pole is the upper, and those who live in the region of it are in the upper hemisphere and to the right, whereas we are in the lower and to the left" (On the Heavens [De caelo], II.2.285b.23–25). For an analysis of this rather unimportant point, see Thomas L. Heath, Aristarchus of Samos (Oxford: Clarendon Press, 1913), pp. 231–232.

40. Columbus: [17]"The author. The arctic pole is above." D’Ailly’s disagreement with Aristotle is based wholly on arguments presented by Oresme in Traitié de l’espere.

41. See the preceding chapter. Although slightly rearranged and altered, this eighth chapter is based almost wholly on Roger Bacon’s Opus maius, Part IV (Burke, I, 310–312).

42. Columbus was greatly interested in arguments demonstrating that the sea between Spain and India was a relatively small one which could be navigated in a short time. The Ymago Mundi, which was a world geography used widely prior to the reintroduction of Ptolemy’s Geography in the fifteenth century, was invaluable to Columbus because it furnished arguments which he could subsequently use to convince others of the feasibility of his plans to sail westward and reach the Orient, the basic objective of his first voyage. As we shall see, chapters 8, 10 and 11 were quite useful in this regard.

Columbus: [24] "Note that in this year of [14] 88, in the month of December, Bartholomew Diaz, captain of three caravels which the Most Serene King of Portugal had sent to Guinea to take land, landed in Lisbon. He reported to the Most Serene King that he had sailed beyond the Yan, having traveled 600 leagues, namely 450 to the south and 250 to the North, and that he had reached a promontory to which he gave the name of "Cape of Good Hope," which we thought to be in Agensinba. By means of an astrolabe he found that in this place he was 45 degrees beyond [or south of] the equinoctial line [or equator] and that this place was 3100 leagues from Lisbon. He pictured and wrote about this voyage league by league on a navigation chart so that he could show it to the eyes of the Most Serene King. I was present at all these things.

"This agrees with the statement of Marinus [of Tyre], whom Ptolemy corrected with respect to his voyage to the Garamantes, where Marinus said he had travelled 27,500 stades beyond the equator. Ptolemy rejects and corrects this. He agrees with Pierre d’Ailly that the waters do not cover three fourths of the earth.

"This agrees that the sea is wholly navigable and that excessive heat is no impediment."

John K. Wright (The Geographical Lore of the Time of the Crusades [New York: American Geographical Society, 1925], p. 41) suggests that the country of the Garamantes is the more modern Fezzan, located in West Central Libya and forming part of the Sahara desert. He goes on to say that "Ptolemy mentions two expeditions that had been made at an unknown period to the south from the land of the Garamantes, one under Septimius Flaccus, who arrived at the country of the Ethiopians after three months’ journey, and the other under Julius Maternus and the king of the Garamantes, a four months’ journey to a country called Agisymba [probably identical with "Agensinba" mentioned above by Columbus—Ed.], abounding in rhinoceroses." It seems that Columbus believed that Bartholomew Diaz’s voyage had penetrated as far south as the expedition from the Garamantes to Agensinba (thought by Columbus to include the Cape of Good Hope) described by Ptolemy. Marinus of Tyre (ca. 90–130), a Greek geographer from whom Ptolemy drew much detailed information, had made the earth excessively large, so that Ptolemy found it necessary to reduce its extent on the basis of an estimate of 180,000 stades as the earth’s circumference. In this marginal comment Columbus cites one instance in which Marinus had greatly exaggerated the estimate of the distance that he had traveled to the Garamantes and where Ptolemy had rightly corrected him. Indeed, the Garamantes, if they really lived in Fezzan, would have been at 27 degrees N latitude, well above the equator.

The broad significance of all this for Columbus lies in the fact that Diaz’s voyage not only confirmed the ancient reports of habitation beyond the equator but also reinforced his belief that the earth is a relatively small and navigable sphere.

43. I have not found such a title amongst the known works of Ptolemy. Perhaps it was some part of one of his treatises which circulated independently.

44. For Ptolemy’s estimate that only one fourth of the world is inhabitable (extending over 180 degrees of longitude and 90 degrees of latitude), see the Almagest, Book II, chapters 1 and 6. Columbus sought to discredit Ptolemy’s estimate, since it implied that the oceans would be too large and formidable to navigate.

45. Neither Aristotle nor Averroes explicitly declares that the inhabitable part of the world occupies more than one fourth of the earth’s surface.

46. Columbus: [24]"Aristotle. Between the end of Spain and the beginning of India there is a small sea navigable in a few days." Actually Aristotle says only that some hold that the Pillars of Hercules (Straits of Gibraltar) and India are connected, since elephants are found at both ends. Nothing is said about the sea being small or navigable. See On the Heavens, II.14.298a.9–15.

Columbus eagerly seized upon all mentions of a narrow ocean in the Ymago Mundi. These he annotated or copied into the margin. See S. E. Morison, Admiral of the Ocean Sea, I, 122–123, for a list of such instances. See also notes 70, 71.

47. According to Roger Bacon, "We must know that Spain in this locality is considered not as hither but as farther Spain, of which certain authors speak, as Pliny in the Questions on Nature [i.e., Natural History], and Merlinus in his prophecy, and Orosius in his book Ormesta Mundi, and Isidore in the fourteenth book of the Etymologies" (Burke, I, 312). In his comment quoted in the preceding note Columbus (like Aristotle; see n. 46) says nothing about the distinction between Hither and Farther Spain. According to Bacon (Burke, I, 312), "Between the Spain so called at present and the Africa so named at this time water did not flow, but the land was continuous in times past, but later the ocean broke through in the low parts of the earth and joined the Tyrrhenian Sea [i.e., the Mediterranean], which flows by the coast of the province of Arragone and of Italy. Therefore Hither Spain extends from the Pyrenees Mountains to Carthage: but Farther Spain crosses the Strait of Gibralter up to the provinces of Africa. Hence it extends beyond Gibralter and reaches the Atlas range." Bacon goes on to explain that although Aristotle did not distinguish between Hither and Farther Spain and spoke only of Spain in general (actually he spoke only of the Straits of Gibralter or Pillars of Hercules), his allusion to elephants applies only to Farther Spain (see n. 46), or Africa, since "it is a fact that elephants abound near the Atlas range." In this manner, Bacon and his predecessors tried to make sense of "elephants in Spain."

48. Columbus: [24]"Pliny. In a not very great time, the Arabian Gulf to the Pillars of Hercules (Gades) has been navigated."

49. Columbus: [24]"Esdras. Six parts are inhabited and the seventh is covered with waters" (III Esdras 6:42). The third and fourth books of Esdras have been considered apocryphal. Since this statement by Esdras was very favorable to Columbus’ claims that a voyage westward would be easily feasible, he sought to confer great respectability and reliability on Esdras (see the next note).

50. Columbus: [24]"Note that blessed Ambrose and Aurelius Augustine and several others took Esdras as a prophet and approved his book, as the extracts from his books (below) reveal; for they do not seem to be apocryphal.

"And with respect to the water, the opinion of Peter the Eater (Petrus Comestor) agrees; for if we consider what we know at present through navigations, this is found to be true. [The last two paragraphs were enclosed by Columbus in a single rectangular box.—Ed.].

"St. Augustine; The City of God.

"Franciscus de Mayronnis in his [book on] [Theological] Truths says in the twelfth truth that after the return of the Jews from Babylon they did not have any prophets after Malachi, Haggai, Zechariah, and Esdras, until the coming of the Savior unless [one counts] Zechariah, father of John, old Simeon, and the most glorious John the Baptist. Finally, in this chapter [May-ronnis says that] a noteworthy thing is understood, [namely] that Esdras was a prophet and his prophecies, although not canonical, seem authentic. And this is confirmed, since blessed Ambrose admits it by accepting the utterance of this prophecy: My son Jesus died and the world is converted.

"Peter the Eater, master of ecclesiastical histories says: The third day God brought together the waters into one place under the firmament even though they could acquire more places. However, since all were continuous in the bowels of the earth, it could be said that they were capable of being brought together, so that the waters, which occupied the whole space of air when in a vaporized state occupied a small space in a solid state; or the earth rises little by little until it encloses the waters as in a vessel; and so the earth appears dry." I have omitted the last section, which continues in the same vein. For the various references to Franciscus Mayronnis (a scholastic at the University of Paris who died in 1325), Peter the Eater, and others, see the appropriate footnotes in Buron I, 210–215.

51.Natural History VIII, 17.

52.Polyhistor seu de mirabilibus mundi IV. The Polyhistor of Solinus, who lived in the third century A.D., was a geographical work based largely on Pliny.

53.Natural Questions VI, 8.

54. Here again, d’Ailly aids Columbus by arguing that the waters on the earth are less extensive than some prominent authors had allowed. In Traitié de l’espere, chapter 37, Oresme had also cited Albategni’s theory.

55. This last paragraph is taken from Oresme, Traitié de l’espere, chapter 31.

56. This chapter is largely a translation of Oresme’s Traitié de l’espere, chapters 33, 34. In chapter 9, d’Ailly had discussed the division of the inhabited part of the earth into seven climes. This was accepted by almost all authors and is found, for example, in Alfraganus (Elementa), Sacrobosco (On the Sphere), Roger Bacon (Opus maius) and Oresme (Traitié de l’espere). Here d’Ailly continues the discussion of the seven climes. See also Selection 1, notes 58 and 59.

57. For instance, Sacrobosco and Oresme.

58. Columbus: [28] "Every degree contains

miles; therefore the whole circuit [or circumference] of the earth is 20,400 miles." S. E. Morison observes that "Columbus notes every mention of the length of a degree, and sometimes writes in the margin ’Not so. A degree is
Roman miles,’ or words to that effect." (Admiral of the Ocean Sea, I, 122). In arguing for the feasibility of a voyage westward, this value of a degree produced a sufficiently small earth to lend credibility to Columbus’ claims. In a part of the present chapter omitted here, Columbus, in marginal comments 30 and 31, emphasizes that
miles per degree is an exact measurement (interestingly, these comments are enclosed in boxes). This particular figure was arrived at by the Arabs in the ninth century.

59. That is, north of the equator.

60. Columbus: [33] "The author proves that there is habitation under the equator and beyond the tropic of Capricorn." See chapter 6 and n. 38, where d’Ailly denies the habitability of the torrid zone. D’Ailly’s source for much of this chapter was Roger Bacon, Opus maius, Part IV. Oresme, Traitié de l’espere, chapter 38, seems also to have been utilized.

61.Natural History II, 8; II, 75, 76; VI, 24, 34, 39.

62.Hexameron IV, 5.

63. Ambrose gives the Greek term askioi, which means literally "those who are without shade."

64. Here again, Ambrose gives the Greek term amphiskioi, which, in the Greek lexicon of Liddell and Scott, is defined as "throwing a shadow both ways, sometimes north, sometimes south, of those who live within the tropics." Thus the inhabitants of this region are sometimes shadowless (see n. 63) and for the rest of the time cast shadows sometimes north and sometimes south; hence are "surrounded by shadows."

65. Pliny, Natural History II.112.5; II.75.3.

66. Haly, De judiciis astrorum (On the Judgments of the Stars), IX, 37; page 406 of the edition by Peter Liechtenstein, Basle 1551 or 1571.

Columbus: [34] "Two cities lie beyond [or below] the equator, one is called Deleit, the other Baraya."

67. Colubmus: [35] "Beyond [or below] the tropic of Capricorn, the region of Pathalis is found which has a port where shadows fall only to the south and the sun is always to the north."

68. VI, 22 and 24.

69. Columbus: [35] "Men came from Taprobane to Rome."

70. Columbus: [36] "Taprobane is opposite India; [and] since it is toward the east opposite [India], it has nations [or peoples]."

[37] "Note that if Taprobane is situated as described above, it would be distant from true west by 58 degrees to the west; for this reason we approve [the opinion] that the sea which separates Spain and India is small" (see n. 46 and n. 71).

71. Columbus: [43] "The limit of the habitable earth in the east and the limit of the habitable earth in the west are quite close and there is a small sea between" (see n. 46 and n. 70).

72. Columbus: [44] "The climes are longer than the astronomers suppose."

73. Condensed and somewhat rearranged, the last two paragraphs are closely akin to chapter 38 of Oresme’s Traitié de l’espere.


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Chicago: Pierre d'Ailly, "The Image or Representation of the World (Ymago Mundi)," A Source Book in Medieval Science, ed. Edmond Buron and trans. Edward Grant in A Source Book in Medieval Science, ed. Edward Grant (Cambridge: Harvard University Press, 1974), 630–639. Original Sources, accessed September 25, 2023, http://www.originalsources.com/Document.aspx?DocID=DC872HZW39F8ADK.

MLA: d'Ailly, Pierre. "The Image or Representation of the World (Ymago Mundi)." A Source Book in Medieval Science, edited by Edmond Buron, and translated by Edward Grant, Vol. I, in A Source Book in Medieval Science, edited by Edward Grant, Cambridge, Harvard University Press, 1974, pp. 630–639. Original Sources. 25 Sep. 2023. http://www.originalsources.com/Document.aspx?DocID=DC872HZW39F8ADK.

Harvard: d'Ailly, P, 'The Image or Representation of the World (Ymago Mundi)' in A Source Book in Medieval Science, ed. and trans. . cited in 1974, A Source Book in Medieval Science, ed. , Harvard University Press, Cambridge, pp.630–639. Original Sources, retrieved 25 September 2023, from http://www.originalsources.com/Document.aspx?DocID=DC872HZW39F8ADK.