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, until he left the army in Syria

•          1500 hoplites and 500 light infantry under Proxenus of Boeotia

•          1000 hoplites under Sophaenetus the Stymphalian

•          500 hoplites under Socrates the Achaean (not to be confused with the philosopher)

•          300 hoplites and 300 peltasts under Pasion the Megaran, until he left the army in Syria

•          1000 hoplites, 800 Thracian peltasts, and 200 Cretan archers (and more than 2000 men

who came from Xenias and Proxenus when they deserted) under Clearchus of Sparta,

•          300 hoplites under Sosis the Syracusan (Anabasis book 1, chp 2, IX)

•          1000 hoplites under Sophaenetus the Arcadian

•          700 hoplites under Chirisophus the Spartan

•          1000 hoplites and 500 Thessalian peltasts under Menon (Anabasis book 1, chp 2, XI)

•          400 Greek deserters from Artaxerxes' army

A hoplite was a citizen-soldier of the Ancient Greek City-states. Hoplites were primarily armed as spear-men and fought in a phalanx formation.

A peltast was a type of light infantry in Ancient Greece who often served as skirmishers.

In addition, they were backed up by a fleet of 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.

When the Ten Thousand start their journey in 401, 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.