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legion,large unit of the Roman army. It came into prominence c.400 B.C. It originally consisted of 3,000 to 4,000 men drawn into eight ranks: the first six ranks, called hoplites, were heavily armed, while the last two, called velites, were only lightly armed. Marcus Furius Camillus is traditionally regarded as the great organizer of the legion. Under Camillus the hoplites were divided into three groups: the hastati (youngest men), the principes, and the triarii (oldest). Within the legion was the cohort, consisting of one maniple of each of the three groups plus 120 velites and a cavalry unit about 30 strong. A legion was composed of 10 cohorts and comprised about 5,000 men. In Caesar's time each legion had a commander who was responsible to the Senate, 6 tribunes, a legate, a prefect, and some 60 centurions. Training was hard, with much difficult drilling to prepare the men especially in shock tactics and for rapid marches. The standard weapons were the spear (pilum) and (after Scipio Africanus Major conquered Spain) the short thrusting sword (gladius). The characteristic emblems of the legions were eagles inscribed SPQR [Senatus Populusque Romanus—the Senate and the people of Rome], and they carried the eagles in triumph over the far reaches of the empire for hundreds of years. Upon the legions rested to a large extent the glory of Rome. They were primarily heavy infantry and were vulnerable to quickly moving cavalry and archers (e.g., the defeat of Marcus Lucinius Crassus at Carrhae) and to guerrilla fighters (e.g., the famous defeat of Varus by the Germans). With the Germanic invasions the legion proved unable to match the barbarian horsemen, rendering it obsolete.
See G. Webster, The Roman Imperial Army of the First and Second Centuries (1969).
the basic organizational unit of the army of ancient Rome.
Originally the entire Roman host was called a legion, which was a slaveowners’ militia numbering about 3,000 infantrymen and 300 cavalrymen from among the propertied citizens; they assembled only in wartime and for military training. In the fifth and fourth centuries B.C. the number of legions was increased from two to four and more. In the early fourth century B.C. a small salary was established for the soldiers. A legion was composed of 3,000 men in the heavy infantry (principes, hastati, and triarii), 1,200 men in the light infantry (velites), and 300 cavalrymen. The different categories were recruited from among different propertied classes of the Roman citizenry and had different armament. The heavy infantry was divided into 30 tactical subunits, called maniples (from 60 to 120 soldiers each, forming two centuries), to which velites were attached. A legion was headed in the republican period by a tribune and in the imperial period by a legate.
In the late second century B.C., Marius abolished the difference in armament of the heavy infantry and the recruitment of different categories of soldiers and changed the organization of the legion by combining every three maniples into one cohort. As a consquence of the ruin of the free peasantry, obligatory military service was abolished, an increased salary was established for the soldiers, and the Roman Army became a professional mercenary army. The number of legions reached 75 under Emperor Augustus; by the end of his reign it was reduced to 25, but the size of the legion was increased to 7,000 men. Each legion was given a number and its own name and had a “banner”—a silver eagle on a pole. When the Roman Empire was divided in the late fourth century A.D., the Eastern Empire had 70 legions and the Western Empire 63.
From the 16th to 19th centuries the term “legion” was applied to various military units in France, Great Britain, Germany, and Russia. The Polish legions were particularly well known.