Roman legion

A Roman legion was the largest military unit in the Roman army.

These units were composed of Roman citizens known as legionaries. They served as the elite heavy infantry for the Roman state. While the legions were the most famous part of the military, they did not make up the whole army. Most of the Roman military actually consisted of auxiliaries. These were non-citizens who provided extra infantry and most of the cavalry.

The organization of a legion changed many times throughout Roman history. In the early Roman Kingdom, forces were organized into groups called centuriae. Each centuria contained roughly one hundred men. During the Republic, the military structure was often influenced by Greek and Macedonian styles. One system used maniples, which were smaller tactical units. Later, the legions were restructured into ten cohorts. A cohort was a larger group made of several centuries.

In the late Republic and early Imperial period, the size of a legion was quite large. A typical legion might have about 4,800 legionaries. These were divided into ten cohorts, with each cohort containing six centuries. In some periods, the first cohort was double-strength. This meant it held about 800 men instead of the standard 480. The total strength of a legion in the Imperial period often reached 5,280 men. This total also included 120 auxiliaries to support the infantry.

Different types of soldiers performed specific roles within the legion. The heavy infantry was the main force of the unit. These soldiers used equipment like bronze helmets, shields, and the gladius, which was a short sword. They also used the pilum, a heavy javelin, to strike enemies from a distance. The equites provided the cavalry, which consisted of about 300 horsemen. They were divided into ten smaller units called turmae. Finally, the velites acted as light infantry. These were often poorer citizens who served as skirmishers using javelins.

The way soldiers were chosen also evolved over time. During the early Republic, the army was organized based on social class and wealth. The poorest citizens fought in the first line of battle. This was known as the Camillan system. By the 3rd century BC, the Polybian system replaced it. This new system organized soldiers by their age and experience rather than their money. This change made the legions more efficient in combat.

History shows that some legions were incredibly long-lived. For example, the Legio V Macedonica was founded by Augustus in 43 BC. This unit remained active for centuries and was in Egypt during the seventh century. However, other legions met sudden ends. In the Varian Disaster of AD 9, three legions—the XVII, XVIII, and XIX—were destroyed. These specific units were never raised again by the Roman military.

As the Roman Empire changed, the legion itself became smaller. By the third and fourth centuries AD, the large formations were broken down. Instead of thousands of men, legions often consisted of only 1,000 to 1,500 soldiers. This change allowed the military to cover more territory. Smaller units were better for guarding long borders. In the East, border guard legions called limitanei may have become even smaller. This evolution helped the military adapt to the needs of a changing empire.