He was born in Athens and became a disciple and friend of Socrates. In 401 he joined the campaign of the Persian prince Cyrus the Younger against Artaxerxes II; when Cyrus was killed north of Babylon, Xenophon led an army of 10,000 Greek mercenaries in their retreat to the Black Sea, a journey of about 1500 km (900 miles). His historical works include the Anabasis, an account of the campaign with Cyrus and its aftermath, and the Hellenica, a history of Greece. Among his other writings are three works concerning the life and teachings of Socrates, and the Cyropaedia, a historical romance about the education of Cyrus the Younger.