The basic organizational unit in the army of Ancient Rome.
The Legion consisted of 5-6 million infantrymen and hundreds of riders. Each legion had its own name and number. The written sources identified approximately 50 different legions, although it is believed that number of legions in each historical crusade never exceeded twenty-eight, but if necessary it could be increased. For a long period of time Roman legioners were probably the most powerful and strong warriors in the whole world. And their armour played for this a pivotal role. Full set of Roman legion armour you can find here.