Map of Persia and the March of the Ten Thousand

A map of Persia, indicating major settlements, regions, and mountain ranges, as well as the march of the Ten Thousand (dotted line).

The Ten Thousand were a group of mercenary units, mainly Greek, drawn up by Cyrus the Younger to attempt to wrest the throne of the Persian Empire from his brother, Artaxerxes II. Their march to the Battle of Cunaxa and back to Greece (401 BC-399 BC) was recorded by Xenophon (one of its leaders) in his work, The Anabasis.

Until shortly after the Battle of Cunaxa, the Spartan general Clearchus was recognized as the commander of the army. When Tissaphernes arrested and executed Clearchus, Proxenus, Menon, Agias (possibly the same person as Sophaenetus), and Socrates, their places were taken by Xenophon, Timasion, Xanthicles, Cleanor, and Philesius, with the Spartan Chirisophus as the general commander.

When the Ten Thousand start their journey in 401 BC, Xenophon tells us that they number somewhere around 10,400. At the time Xenophon leaves the Ten Thousand in 399, their numbers had dwindled to nearly 6000.

Description text from Wikipedia under the GNU Free Documentation license.