Marian Reforms - Subsequent Modifications

Subsequent Modifications

The cohort legions of the late republic and early empire are often called Marian legions. Following the Battle of Vercellae in 101 BC Marius granted all Italian soldiers Roman citizenship. He justified this action to the Senate by saying in the din of battle he could not distinguish Roman from ally. This effectively eliminated the notion of allied legions; henceforth all Italian legions would be regarded as Roman Legions. Thus the three different types of heavy infantry (the Hastati, the Principes and the Triarii, which composed the pre-Marian Roman armies) were replaced by a single, standard type of legionary based on the Principes.

The role of allied legions would eventually be taken up by contingents of allied/auxiliary troops, called Auxilia. Each legion had a same size or near same size Auxilia (auxiliary), which contained specialist units, engineers and pioneers, artillerymen and siege craftsmen, service and support units plus units made up of non-citizens (who were granted Roman citizenship upon discharge) and undesirables. These were usually formed into complete units such as light cavalry, light infantry or velites, and laborers. There was also a reconnaissance squad of 10 or more light, mounted infantry called speculatores who could also serve as messengers or even as an early form of military intelligence service.

During these reforms, the legions were also organized into permanent cohorts for the first time. Prior to this cohorts had been temporary administrative units or tactical task forces of several maniples, even more transitory than that of the legions of the early republic themselves. Now the cohorts were six to ten permanent units, composed of five to eight centuries each led by a centurion assisted by an Optio, a soldier who could read and write. These came to form the basic tactical unit of the legions. The senior centurion of the legion was called the primus pilus, a career soldier and adviser to the legate; he was generally 50 years of age or older. There were also additional officers assigned to each legion, an Aquilifer, Imaginifer (Imperial Rome only), a Tesserarius, and a Cornicen. The aquilifer was in charge of the legion standard, so there was only one per legion. The imaginifer carried an image of the deified emperor (whichever one was in power at the time). The tesserarius was in charge of the guard outposts for each century. The cornicen was crucial in the heat of battle, as he blew the formation, attack, withdrawal, and many other notes. This was the only way legionaries and their officers could hear or issue orders in the din of battle.

Every legion had a baggage train of 500–550 mules, or about 1 mule for every 10 legionaries. To keep these baggage trains from becoming too large, Marius had each man carry as much of his own equipment as he could, including his own armor, weapons and 15 days' rations or about 50–60 pounds of load total. To make this easier, he issued each legionary a forked stick to carry his load on his shoulders. The soldiers were nicknamed Marius' Mules (muli mariani in Latin) due to the amount of gear they had to carry themselves.

A typical legion of this period had around 5,000-6,000 legionaries as well as a large number of camp followers, servants and slaves. Legions could contain as many as 6,000 fighting men divided among several cohorts. Numbers would also vary depending on casualties suffered during a campaign; Julius Caesar's legions during his campaign in Gaul often only had around 3,500 men and on one occasion during his civil war against Pompey the Great he had to join two of his battle-reduced legions together to achieve the strength of one conventional legion.

Hundreds of years later, under the Emperor Diocletian and his successors, new legions raised for the field armies, as opposed to those stationed along the frontiers, were recruited to only about 1,000 men and were, therefore, the size of military auxiliary cohorts. This was a response to the logistical needs of the late Empire: the smaller units were more easily dispatched as needed to trouble spots than were the older, larger units, and they were no longer made up exclusively of fully armored heavy infantry. Instead, they often consisted of light infantry or archers. Except with regard to Roman citizenship (and even then not always), they were, in fact, no longer sharply distinguished, if distinguished at all, from auxiliary units raised from barbarians within and without the Empire. These later legions (comitatenses) should not be confused with the legions of heavy infantry of the earlier empire.