The Roman Army was a highly organized military force that played a crucial role in the expansion and protection of the Roman Empire. It was composed of professional soldiers known as legionaries, who served for about 25 years. Each legion typically consisted of around 5,000 men, divided into smaller units called centuries. Roman armies were known for their discipline, training, and advanced tactics. They utilized various formations, such as the testudo, to protect themselves during battles. The army also included auxiliary troops, who were non-citizen soldiers that provided additional support and specialized skills, enhancing the overall effectiveness of the military.