Roman legions formed the core of the Roman army. Each legion of heavily armed infantry consisted of some 5,000 Roman citizen men. The legionary soldier was recruited aged 18–20 for a period of 25 years. Good promotion prospects and a pension of a land grant ensured a constant supply of recruits. The rest of the army—infantry and cavalry—was made up of auxiliaries (the auxilia, or ‘aids’) who did not have to be Roman citizens. Auxiliaries were sometimes provincial specialists, such as the famed Syrian archers.

The legions which invaded Britain in ad 43 under the command of Aulus Plautius were the II Augusta, IX Hispana, XIV Gemina, and XX Valeria. With auxiliaries, the force totalled some 40,000 men. The II Adiutrix replaced the XIV Gemina during a major reorganization of military dispositions in the 60s/70s ad. Each legion was based in a legionary fortress. The II Augusta, for example, was based variously at fortresses in Exeter, Gloucester, and Caerleon.

Extensively excavated forts include those of Hadrian's Wall, notably Birdoswald, Vindolanda, Chesters, and Housesteads. Such research indicates that the Roman army which invaded Britain in ad 43 was very different in structure from that which abandoned the province in ad 410.

Eleanor Scott

legions, Roman. See Roman legions.