Claudius Ptolemaeus, better known as Ptolemy (circa 100–178 AD) made many important contributions to geography and spatial thought. Ptolemy’s most famous written works are the Almagest, a textbook of astronomy in which, among other things, he laid the foundations of modern trigonometry; the Tetrabiblos, a compendium of astrology and geography; and Geographica (his guide to “”Geography””), which compiled and summarized much of the geographic information accumulated by the Greeks and Romans up to that time.