A legion is a large military unit historically used by the ancient Romans. Typically, a Roman legion consisted of about 4,000 to 6,000 soldiers, organized into smaller groups called cohorts. Legions were known for their discipline, training, and effectiveness in battle, playing a crucial role in the expansion of the Roman Empire. In modern contexts, the term "legion" can refer to any large group of people united for a common purpose. For example, the American Legion is a veterans' organization that supports former military personnel and their families. The word can also describe a vast number of individuals, as in "a legion of fans."