The first cohort contains the aquilifer, the bearer of the legions eagle standard. The primary symbol of roman power and an inspiration for all roman soldiers nearby.

The first cohort represents the elite of the whole legion, it contains the best legionaries and also the aquilifer, the bearer of the eagle standard, the primary symbol of roman power. Nothing can be more dishonouring than its loose and the eagle’s presence inspire the legionaries nearby, especially if it’s carried ahead of the advancing lines into the heart of battle.

Legionary infantry is still the backbone of the imperial army and it is now easily considered as the most disciplined and most versatile heavy infantry in the world. Their broad training and famous discipline offers them many tactical possibilities in battle, but normally legionaries will fight in the traditional way: throw their pila as soon as the enemy comes in range to soften his formation and then engage at close quarters. While not designed to do so, the pilum can be used like a normal spear as well to make it possible for the legionaries to defend themselves more readily against heavy cavalry attacks.

The legion's high quality equipment has become one of the great strengths of the Roman infantry, besides their strict discipline. Most legionnaires are now equipped with Coolus bronze helmets, shirts of lorica hamata or squamata (chain or scale mail) as main body armour and a half ovular scutum, slightly lighter than old republican oval type, while being armed with a type Mainz gladius, two pila and a short dagger called a pugio.

Historically, standards were not only simple tools to control units, but almost sacred and religiously admired items for the imperial army. They were the center of the roman military’s ideology, symbolizing the identity of an unit as well as the virtues and traditions of the army. The most prestigious of them all was the golden aquila, the legions eagle standard, representing not only the whole legion but also the might and authority of the Senate and the People of Roma.
The first cohorts were the legion’s elite units and its centurions, the primi ordines, ranked above the others. According to the 4th century military theorist Vegetius a minimum height requirement only for ala and legionary first cohorts, of at best six (1,77m) or at least 5,5 roman feet (1,62m) had existed. In the early principate the cohort’s size was increased to 800 men, now organized in five double strength centuries. The first cohort was commanded by the primus pilus, originally the leading centurion of the triarii maniple. Since the Augustan era, this become one of the most important position in a legion, usually limited to one year. His centuria guarded the eagle standard and usually the primus pilus was also a part of commanding general’s council of war. Normally this rank was the most prestigious, respected and well paid position a ordinary legionary could hope to achieve, that brought with it the rise to equestrian rank at the end of his service. If still young enough, a primipilaris had excellent chances to continue his career in leading positions within imperial service.

Experts in siege warfare, artillery, and other engineering tasks could be found in the ranks of the legion, and all contubernia, the eight men strong basic logistical units of the army, were equipped with tools and valli for the fast construction of field fortifications. To reduce the legion's vulnerable baggage train and increase the mobility of the troops, the legionnaires had to carry as much of their equipment as possible by themselves; nearly 50 Kg. As a welcomed side effect this gave them, combined with their regular training, an unrivalled endurance.

In the early principate the organisation of the legion slightly changed again by attaching a small group of 120 horsemen. They operated as scouts and messengers, screened the legion on the march and some of them formed the bodyguard for the legatus legionis, the legions senatorial commander.

During the decades of his rule following the end of the civil war, Augustus reformed the imperial army significantly and created a standing army with 28 legions as its core. In many fields a systematic approach replaced the improvisation of the late republican era. Most important was that the auxilia, with its indispensable cavalry and archer units, became a regular arm of the professional army and its second base.

The length of service for all soldiers was finally set to 26 years for fleet soldiers, 25 years for soldiers of the auxilia, 20 years for legionaries, and 16 years for praetorians. After their discharge they received a cash bonus, the praemia militare, or a small piece of land. The veterans from the auxilia and the fleet were rewarded with Roman citizenship, and a diploma to prove it. Also, medical treatment was improved and all units were now supplied with physicians.