Claudius Ptolemy (ca 100 — ca 170) was a mathematician and astronomer who lived in the Roman province of Alexandria. Alexandria was a great place of learning and was particularly famous for its library. Ptolemy’s main work on geography is a compilation of coordinates and place names, as well as a description on how to create maps by using a grid that gives each place a unique set of points, a location. This was all contained in one book, the Geography. As with any other work of human knowledge, the book reflects information and ideas that existed at the time. It seems that Ptolemy used a treatise by Marinus of Tyre, now lost, but we can also say that the book is a manifestation of the Greco-Roman tradition of geography and cartography. Ptolemy is also said to be the author of other important treaties, including the Almagest, on astrology.