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.

According to Xenophon, the Ten Thousand were composed of:

• 4000 hoplites under Xenias the Arcadian
• 1500 hoplites and 500 light infantry under Proxenus the Boeotian
• 1000 hoplites under Sophaenetus the Stymphalian
• 500 hoplites under Socrates the Achaean
• 300 hoplites and 300 peltasts under Pasion the Megaran
• 1000 hoplites, 800 Thracian peltasts, and 200 Cretan archers under Clearchus the Spartan
• 3000 hoplites under Sosis the Syracusan
• 1000 hoplites under Sophaenetus the Arcadian
• 700 hoplites under Chirisophus the Spartan

In addition, they were backed up by a fleet on 35 triremes under Pythagoras the Spartan and 25 triremes under Tamos the Egyptian, as well as 100,000 Persian troops under Ariaeus the Persian (although Xenophon lists them as 100,000, most modern historians believe Ariaeus' troops were only around 20,000).

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.