The Legatus Legionis was not the highest rank in the Roman army. It was an important position, but the supreme command belonged to officers holding imperium, such as consuls, proconsuls, and later the emperor, who were called imperatores. The legatus legionis served as the commanding officer of a legion, often delegated authority by an imperator or provincial governor.
In the Roman military hierarchy, supreme command was tied to the concept of imperium. This was a legal and military authority granting the right to command troops and to enforce discipline, even capital punishment. Only certain elected magistrates, such as consuls and praetors, held imperium.
These magistrates, also called imperatores, wielded ultimate military authority during their term. The Senate could extend their command beyond a single year, creating proconsuls or propraetors. In some cases, commanders like Scipio Africanus could receive proconsular commands without having held prior office, known as imperator sine magistratu.
Because imperatores commanded large forces, they appointed subordinate officers to assist them. Among these were military tribunes (young officers at the start of their careers) and legati (legates). The legatus was a trusted lieutenant, often a peer or former consul, appointed to carry significant responsibility.
The legatus legionis acted as the commander of a legion, overseeing the day-to-day military operations of about 5,000 infantry and supporting cavalry. This officer executed the imperator’s orders on the battlefield and managed legion logistics.
Unlike military tribunes, legates were experienced men with high social status and political connections. These officers sometimes also oversaw detachments or specific tasks, and they served on the imperator’s military council, advising strategic decisions.
During the late Republic and into the Empire, the emperor assumed overall command of armed forces. Augustus received imperium proconsulare maius, granting him authority over almost all provincial armies. He never commanded forces directly but ruled through his appointees, the legati Augusti pro praetore.
These provincial governors exercised delegated authority on the emperor’s behalf. Although they did not possess imperium in their own right, they acted as generals leading forces in their provinces. Their powers surpassed those of a legion’s legatus but remained subordinate to the emperor.
| Rank or Role | Authority | Function |
|---|---|---|
| Imperator (Consul/Proconsul) | Holds full imperium | Supreme commander of armies and legions |
| Legatus Augusti pro praetore | Delegated imperium from emperor | Provincial governor and army commander |
| Legatus Legionis | Appointed by imperator or governor | Commander of a single legion |
| Military Tribunes | Junior officers | Assist legion command, early career roles |
The legatus legionis had significant day-to-day command within the legion. However, the role itself was subordinate to officers holding imperium, such as consuls or provincial governors. The term “legatus” could refer to any senior officer appointed by the imperator with delegated command powers, but it did not confer highest military rank.
In the Imperial period, the emperor reigned as the ultimate imperator, with legati acting as his delegates below the provincial level. Therefore, while a legion’s legatus was an important commander, he was not the highest-ranking officer in the Roman military structure.
- The highest command belonged to magistrates with imperium, mostly consuls or proconsuls, and later the emperor.
- The legatus legionis was the commander of a legion but subordinate to officers with imperium.
- Legati were trusted delegates who could command legions or provinces on behalf of an imperator.
- In the Empire, provincial governors named legati Augusti pro praetore exercised delegated imperium.
