Group of a prescribed size with a specific combat role within a larger military organization. The chief units in the ancient world were the Greek phalanx and the Roman legion. Modern units originated in the 16th–18th century, when professional armies reemerged in Europe after the end of the Middle Ages. Since then the basic unitscompany, battalion, brigade, and divisionhave remained in use. The smallest unit today is the squad, which has 7–14 soldiers and is led by a sergeant. Three or four squads make up a platoon, and two or more platoons make up a company, which has 100–250 soldiers and is commanded by a captain or a major. Two or more companies make up a battalion, and several battalions form a brigade. Two or more brigades, along with various specialized battalions, make up a division, which has 7,000–22,000 troops and is commanded by a major general. Two to seven divisions make up an army corps, commanded by a lieutenant general, which with 50,000–300,000 troops is the largest regular army formation, though in wartime two or more corps may be combined to form a field army (commanded by a general), and field armies in turn may be combined to form an army group.
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