Primus pilus
Overview
The term "Primus Pilus" or "First Spear" was an official rank within the structure of the Roman military. This position was held by the most senior centurion in a Roman legion, leading the first cohort, which was the largest and most prestigious cohort in the legion. The Primus Pilus was directly under the command of the legate (legion commander) and was considered the highest-ranking centurion.

Role and Responsibilities
The Primus Pilus had a variety of responsibilities within the legion. They were in charge of the first cohort, which consisted of about 800 men, five times the size of the other cohorts in the legion. This cohort was made up of the best soldiers in the legion, and the Primus Pilus was expected to lead them effectively in battle.
In addition to their military duties, the Primus Pilus also had administrative responsibilities. They were in charge of the legion's finances and were responsible for ensuring that the soldiers were paid. They also had a role in discipline, and could punish soldiers for infractions.
Career Progression
The position of Primus Pilus was usually held by a veteran centurion who had shown exceptional skill and bravery in battle. It was a prestigious position, and many centurions aspired to become the Primus Pilus. However, the position was not permanent and was usually held for a period of one year.
After serving as Primus Pilus, a centurion could be promoted to higher ranks, such as tribune or even legate. Some former Primus Pilus went on to have successful political careers, as the position was seen as a stepping stone to higher office.
Historical Significance
The role of the Primus Pilus was crucial in the Roman military system. They were the link between the legion's soldiers and its commanding officers, and their leadership was key to the legion's success in battle. The Primus Pilus was often the most experienced soldier in the legion, and their knowledge and skills were invaluable.
The position of Primus Pilus also had social significance. In Roman society, military service was highly respected, and the Primus Pilus was seen as a role model for younger soldiers. The position was also a stepping stone to higher office, and many former Primus Pilus went on to have successful political careers.