Claudius Ptolemaeus

Claudius Ptolemy lived in Alexandria in the second century AD (c. 100–170). He was a mathematician, astronomer, geographer, and astrologer whose works dominated their respective fields for over a millennium.

His astronomical masterwork, the Almagest, presented a geocentric model of the universe so mathematically sophisticated that it was not superseded until Copernicus. His Geography provided coordinates for thousands of places across the known world and established the conventions of cartography. But the Tetrabiblos (Four Books), his treatise on astrology, was arguably the most widely read of all his works in the medieval period.

The Tetrabiblos is a systematic defence and exposition of astrology as a natural science. Ptolemy argues that celestial bodies influence terrestrial events through physical emanation, not supernatural decree, and attempts to place astrological practice on a rational, naturalistic foundation. The work covers the effects of planetary configurations on weather, nations, and individuals, and was the standard astrological textbook for Arabic, Byzantine, and Latin scholars for centuries. Modern readers may find the content dubious, but the intellectual rigour of the attempt is impressive.