Claudius Ptolemy (c.100—c.170) was an Egyptian astronomer, mathematician, and geographer. Though of Greek descent, he lived and worked in the Roman city, Alexandria. Not much is known about the life of Ptolemy, but his most famous work is the Almagest. Ptolemy believed that the motion of heavenly bodies could be explained in mathematical terms. In the Almagest, he argues that the Earth is a stationary sphere and the stars, moon, and sun all rotate around it at a uniform rate.