**Proclus** was a Greek philosopher who became head of Plato's Academy and is important mathematically for his commentaries on the work of other mathematicians.

- Proclus was brought up at Xanthus, on the south coast of Lycia, where he attended school.
- Proclus was not entirely satisfied with the education he was receiving in philosophy in Alexandria so, while still a teenager, he moved from Alexandria to Athens where he studied at Plato's Academy under the philosophers Plutarch of Athens and Syrianus (a pupil of Plutarch).
- He progressed from being a student at the Academy to teaching there then, on the death of Syrianus, Proclus became head of the Academy.
- At the Academy Proclus appears to have been well off and to have helped his friends and relations financially.
- Proclus was to remain as head of the Academy until his death.
- A man of great learning, Proclus was regarded with great veneration by his contemporaries.
- Other developers of these ideas were Plutarch and Syrianus, the teachers of Proclus.
- Proclus wrote Commentary on Euclid which is our principal source about the early history of Greek geometry.
- for Proclus the "Elements of Euclid" had the good fortune not to be contradicted either by the Chaldean Oracles or by the speculations of Pythagoreans old and new.
- Proclus had access to books which are now lost and others, already lost in Proclus's time, were described based on extracts in other books available to Proclus.
- The notes on the postulates and axioms are preceded by a general discussion of the principles of geometry, hypotheses, postulates and axioms, and their relation to one another; here as usual Proclus quotes the opinions of all the important authorities.
- Another interesting part of Proclus's commentary is his discussion of the critics of geometry.
- Proclus also wrote Hypotyposis, an introduction to the astronomical theories of Hipparchus and Ptolemy in which he described the mathematical theory of the planets based on epicycles and on eccentrics.
- Nothing here is original and Proclus is proving results first given by Hipparchus and Ptolemy.
- However, although Proclus believed that this theory should be studied by his students at the Academy, he was not uncritical, suggesting that the theory was overly complicated and also that it was an ad hoc theory with no reason to explain its various parts.
- In his astronomical writings, Proclus described how the water clock invented by Heron could be used to measure the apparent diameter of the Sun.
- Proclus's method can be used at the equinox.
- Among Proclus's many works are Liber de causis (Book of Causes), Institutio theologica (Elements of Theology), a concise exposition of metaphysics, Elements of Physics, largely giving Aristotle's views, and In Platonis theologiam (Platonic Theology) giving Plato's metaphysics.

Born about 411, Constantinople (now Istanbul), Byzantium (now Turkey). Died 17 April 485, Athens, Greece.

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Ancient Greek, Astronomy, Geometry, Origin Turkey, Physics, Puzzles And Problems, Special Numbers And Numerals

**Oâ€™Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive