In most armies, a body of troops headed by a colonel and divided into companies,
French {{link=cavalry">cavalry units were called regiments as early as 1558. In early U.S. service, as in European armies up to that time, the usual number of companies in a regiment was 10. Early in the 19th century, Napoleon divided the regiments of the French army into three battalions each, and in 1901 the U.S. Army adopted the three-battalion infantry regimental system.