Tumen, or tümen ("unit of ten thousand";Old Turkic: tümän; Mongolian: , tümen;Turkish: tümen; Hungarian: tömény), was a part of the decimal system used by the Turkic peoples and Mongol peoples to organize their tribal life and armies. Tumen is a social and military unit of 10,000 households and soldiers.
It was thought that the same kind of military organization was used by the Magyars during the conquest of Hungary. According to Ahmad ibn Rustah (c. 930), a Persian explorer and geographer relying on second-hand information, the "Magyars are a race of Turks and their king rides out with horsemen to the number of 10,000 and this king is called Kanda". However, the Magyars were linguistically Finno-Ugric-speaking peoples and did not speak Turkic. Modern scholarship finds that the Magyar/Hungarian cavalry units were called banderia and dundar and not organized in units of 10,000.
In Genghis Khan's military system, a tumen was recursively built from units of 10 (aravt), 100 (zuut) and 1,000 (mingghan), each with a leader reporting to the next higher level. Tumens were considered a practical size, neither too small for an effective campaign nor too big for efficient transport and supply. The military strategy was based on the use of tumens as a useful building block causing reasonable shock and attack.
Tümen is a military unit which is still used in the Turkish Army, consisting of 6,000 to 10,000 soldiers. Its commander is a tümgeneral in the Army and Air Forces and a tümadmiral in the Naval Forces. It is the equivalent of a modern division.