Clearchus (klēär´kəs), d. 401 BC, Spartan officer, celebrated as the leader of the Ten Thousand. Sent in 410 to govern Byzantium, he made himself unpopular by his harsh discipline, and Alcibiades took the city in 408 BC Clearchus later returned and made himself virtual ruler, thereby incurring the anger of the Spartans, who forced him to leave (403). He sought refuge with Cyrus the Younger of Persia, who used him to recruit and later command the Greek mercenary force in support of Cyrus' claim to the throne. At Cunaxa, Clearchus fought boldly, but Cyrus' forces were defeated. After the battle he led the Greek force (the Ten Thousand) in retreat, but was lured into a conference by Tissaphernes and treacherously murdered. The story of the retreat was made famous by Xenophon.