The Roman legions were the primary military units of the ancient Roman Empire. Each legion typically consisted of about 4,500 to 6,000 soldiers, known as legionaries, who were well-trained and heavily armed. The legions were organized into smaller groups called cohorts and centuries, allowing for effective command and control during battles. Legions played a crucial role in expanding and protecting the Roman Empire. They were known for their discipline, organization, and innovative tactics, which helped them conquer vast territories. The legacy of the Roman legions influenced military strategies in many cultures throughout history.