Clearchus, the son of Rhamphias, was a Spartan general and mercenary.

Born about the middle of the 5th century BC, Clearchus was sent with a fleet to the Hellespont in 411 and became governor of Byzantium, of which town he was proxenus. His severity, however, made him unpopular, and in his absence the gates were opened to the Athenian besieging army under Alcibiades (409).

Subsequently appointed by the ephors to settle the political dissensions then rife at Byzantium and to protect the city and the neighbouring Greek colonies from Thracian attacks, he made himself tyrant of Byzantium, and, when declared an outlaw and driven thence by a Spartan force, he fled to Cyrus.

In the "expedition of the ten thousand" undertaken by Cyrus to dethrone his brother Artaxerxes Mnemon, Clearchus led the Peloponnesian delegation of the Army of the Ten Thousand, who formed the right wing of Cyrus’s army at the battle of Cunaxa (401). On Cyrus’s death Clearchus assumed the chief command and conducted the retreat, until, being treacherously seized with his fellow-generals by Tissaphernes, he was handed over to Artaxerxes and executed .

In character he was a typical product of the Spartan educational system, He was a warrior to the finger-tips, and his tireless energy, unfaltering courage and strategic ability made him an officer of no mean order. But he seems to have had no redeeming touch of refinement or humanity.

Michael Curtis Ford, Ten Thousand: A Novel of Ancient Greece , Thomas Dunne Books; 1st ed edition (July 13, 2001)

Battle of Cynossema