Claudius Ptolemaeus (Greek: Κλαύδιος Πτολεμαίος Klaúdios Ptolemaîos; after AD 83–c.168), known in English as Ptolemy (pronounced /ˈtɒləmɪ/), was a Roman mathematician, astronomer, geographer and astrologer. He lived in Roman Egypt, and was probably born there in a town in the Thebaid called Ptolemais Hermiou; he died in Alexandria around 168 AD.

Ptolemy was the author of several scientific treatises, three of which would be of continuing importance to later Islamic and European science. The first is the astronomical treatise now known as the Almagest (in Greek, Η Μεγάλη Σύνταξις, "The Great Treatise", originally Μαθηματική Σύνταξις, "Mathematical Treatise"). The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is the astrological treatise known in Greek as the Apotelesmatika (Ἀποτελεσματικά), or more commonly in Latin as the Tetrabiblos ("Four books"), in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day.

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