The Mongol military unit consisting of 10,000 soldiers was called a tumen. The word belonged to the decimal organization used by Turkic and Mongol peoples, in which armies were grouped into units of 10, 100, 1,000, and 10,000.
Under Genghis Khan, the system helped organize a highly disciplined and mobile army. Smaller units included the arban, usually ten soldiers, and the mingghan, usually 1,000. Ten mingghans formed one tumen, commanded by a tümen-ü noyan, or commander of ten thousand.
A tumen was an organizational ideal, not always an exact headcount. Campaign losses, allied troops, recruits, and logistical needs meant that some tumens were understrength. Mongol armies often operated in groups of three tumens, though a single tumen could also be deployed independently.
The term should not be confused with mingghan, which represented the smaller 1,000-man level. Modern references may spell the answer tümen or tümen, but Tumen is the standard English form.