In the Gathering Storm expansion, the Legion requires 10 Iron to train.
The Legion's raw strength and ability to create fortifications makes it an invaluable tool in early-game expansion. Capturing multiple cities in a single campaign becomes much easier, since defenses can be constructed immediately around a captured city.
Dedicated completionists should refrain from upgrading at least one Legion and keep its single build charge intact until late in the game, then use it to clear the fallout left behind by a nuclear weapon. Doing so will unlock an achievement.
The legion was the most efficient and effective fighting force in history … well, in its time anyway. A fully-equipped, fully-staffed Roman legion could march across any terrain, laying a road as it did, built a fortified camp at the end of it, and then take any foe or take any wall. During the Empire a legion was composed of infantry, recruited exclusively from Roman citizens, along with the cooks, armorers, engineers, artillerists, medics and command staff (as well as the usual camp followers and sutlers) necessary to operate in the field for years at a time. The light infantry, archers, scouts, and cavalry were generally auxiliaries, provincial non-citizens (those who survived to be honorably discharged gained citizenship) assigned to a legion as necessity dictated. Extremely disciplined (usually), the legion’s heavy infantry were armed with pilum (throwing spear) and gladius (short sword) and conquered most of the known world (granted, a bunch of barbarians and decaying empires) at the time.
Missed That Day in History Class
Clear nuclear contamination with a Roman Legion