Legion

A legion was a military unit in the army of ancient Rome. It consisted of between 3000 and 6000 infantrymen, all Roman citizens who had volunteered for service as professional soldiers. Each legion also had a small number of cavalry (to act as scouts, couriers, etc.): most of the cavalry was provided by Rome’s allies, who also supplied large numbers of soldiers to serve in non-legionary infantry units. (These latter and the cavalry are typically referred to as auxilia, i.e., auxiliary troops.). Legionary soldiers were expected to serve, altogether, 25 years, after which they were able to retire on a state pension. During the period of the Roman Empire, i.e., from the end of the first century BCE to the fifth century CE, the number of legions was in the high 20s, but never exceeded 30. Each was identified by its number and a name (e.g., II Augusta, IX Hispana, XIV Gemina, etc.), and had its own standard which bore the symbol of the Roman eagle. In the earlier part of the first century CE legionary soldiers came overwhelmingly from Italy and southern France, but in later centuries with the extension of Roman citizenship they came increasingly from other parts of the Roman Empire.

The word legion is used in several other ways. It may refer to:

any large military force or army, such as the French Foreign Legion (created in 1831 for foreign nationals who wished to serve in the French Armed Forces);

an association or organisation for retired servicemen and women, such as the British Legion (formed in 1921 to care for those who had suffered as a result of service in the First World War, either servicemen and women themselves or their dependants); or

a very large number of individuals, as in the translation of the reply to Jesus’ question in the King James version of the Bible to the "unclean spirit" in Mark's Gospel, ch. 5: v 9: "My name is Legion: for we are many." There is an intermediate understanding, between 'a military unit' and 'a large number, possible in Matthew 26:53: "Thinkest thou that I cannot now pray to my Father, and he shall presently give me more than twelve legions of angels?"

The word legion is more widely used as an adjective to mean ‘very many, numerous’, though usually in postposition, i.e., after the noun it qualifies, as in ‘Her admirers are legion’ or ‘The possibilities, though legion, are fraught with risks’.

The two words for a member of a legion, namely, legionary and legionnaire, are not interchangeable. A soldier in a Roman legion is a legionary, while a member of the French Foreign Legion, the British Legion, etc., is a legionnaire. (Legionary may also be used as an adjective, as in the first paragraph above.)

Legionnaire’s (or Legionnaires’) disease, a sometimes fatal infection, caused by the bacterium Legionella pneumophila, and contracted through breathing contaminated water vapour from, e.g., cooling towers or showers, is so called because the first cases of the disease were found, in 1976, amongst those who had attended a convention of the American Legion at Philadelphia).

Note on pronunciation: The word legion is pronounced LEE-jern, IPA: /'liː dʒən/, though its Latin original, lĕgio, has a short ‘e’.