AI overview
A Roman legion was a large military unit in the ancient Roman army, typically consisting of several thousand heavily armed soldiers organized into smaller companies. Legions were central to Rome's ability to conquer and maintain control over a vast empire, making them one of history's most effective and influential military forces.
AI-generated from the Wikipedia summary — may contain errors.
Article
The Roman Empire under Hadrian (r. 117–138), showing the legions deployed in its senatorial provinces
Campaign history