Greek philosophers
Euclid of Megara
Eucleides of Megara was a Greek philosopher who was born around 450 BC in Megara (according to other sources in Gela, Sicily) and died in 368 BC. He was one of the earliest pupils of Socrates and the founder of the Megarian school of philosophy.
Little is known about the life of Euclid of Megara. He was supposed to be studying the writings of the Eleatic Parmenides.
He learned from Socrates very often right in Athens until the Athenians banned all people from Megara (Megara was an ally of Sparta) from entering their city. Anyone who violated this ban would lose his head. Eucleides solved this by always walking the 20 miles from Megara to Athens at night in female disguise so that he could at least listen to the nightly deliberations of Socrates. He would then return home again in the morning.
He also went to Socrates in prison, even on the day of his execution. After the death of Socrates, some of his disciples took refuge with Euclid in Megara. Among them were Plato, Ichthyas, Kleinomachos of Thurii, and probably Eubúlidês of Miletus.
His most important surviving quote is: "Most foolish men reject slave food and dress, but they do not shun slave manners." No other quotes or writings have survived. His works were to be based on the teachings of Socrates, but also on the ideas of the Eleatic school. The teachings of Euclid also influenced the aforementioned Plato.
Euclid and his school are credited with an eristic mentality. That is, the art of argument and the art of discussion. They were concerned with fallacies and paradoxes, thus referring to the influence of the Eleatics. Gradually, logical thinking became predominant, and so the followers of this school greatly enriched the field of propositional logic and in many cases influenced Stoic logic.