Euclid of Megara (/ˈjuːklɪd/; also Euclides, Eucleides; Greek: Εὐκλείδης ὁ Μεγαρεύς; c. 435 – c. 365 BC)[a] was a Greek Socratic philosopher who founded the Megarian school of philosophy. He was a pupil of Socrates in the late 5th century BC, and was present at his death. He held the supreme good to be one, eternal and unchangeable, and denied the existence of anything contrary to the good. Editors and translators in the Middle Ages often confused him with Euclid of Alexandria when discussing the latter's Elements.