The earliest surviving version of Tetrabiblos is the paraphrase attributed to Proclus the Philosopher (412-485). Tetrabiblos (literally, "four books") was long thought to be a complete survey of Greek astrology. Recent research suggests this not to be the case, but Ptolemy'’s work remains the foundation of western astrology. In particular, his persuasive use of the Tropical Zodiac, rather than the Sidereal, changed western astrology forever.