Since its creation, the army of ancient Rome has undergone many transformations. As the Roman state took form, its military was being shaped by the wealthiest citizens. In time this trend was reversed, as members of the poorest social strata became prevalent in the Roman army. It took its final shape in the 2nd century B.C.E, when it became professional, and the citizens started considering military service an occupation.
In the 1st century B.C.E. the army became sole vessel of power in Roman state. Ambitious leaders like Sulla, Pompey the Great, Julius Caesar or Augustus used the legions to expand the borders of Roman state considerably. The Mediterranean became the Empire’s inner sea.
Modern Roman army also largely contributed to the outbreak of civil war in 1st century B.C.E. The consuls came to consider professional army to be their personal guard. The soldiers, dedicated to their commander, went on to regard him as a true leader (Pompey the Great, Gaius Julius Caesar). All this resulted in a rivalry for the position of the most powerful man in the country, who would decide the future of the “inept republic” In a way, the professional army was the force behind the creation of a new form of government, the principate During the Empire period, entire Roman army was under sole command of the emperor.
The creator of a permanent, levy-based army was Augustus. The regular army, which by the end of Augustus’ rule consisted of 25 legions, was stationed in border provinces (mostly along Rhine and Danube). Later the number of legions increased to 30, and additional support troops (auxilia) came into existence. Overall army count was up to around 250 000 soldiers. Under the rule of Julio-Claudian dynasty (27 – 68 B.C.E.) recruits mostly originated from among the citizens of Italy.
With the rule of Vespasian (69-79 C.E.) came recruitment from among the inhabitants of provinces, and after Hadrian (117-138 C.E.) residents would serve in the province from which they originated. The auxilia units consisted of non-citizens, who were awarded full civic rights upon completion of their tour of duty which lasted 25 to 30, but upon some instances even 40 years. Praetorians, who were always stationed in the immediate vicinity of the city of Rome, were at an advantage. Other special troops kept order in Rome – urban cohorts and firemen (cohortes urbanae and cohortes vigilum. Upon completing their tour of duty the veterans would receive severance pay and plots of land, where they would settle down, usually near their former legions.
After the Empire was established, the army became the foundation of the emperors’ rule, while also playing an increasing role as a political factor, often prevailing in the inner workings of the state. The reforms of Diocletian (284-305 C.E.) and Constantine the Great (306-337 C.E.) divided the Roman army into border troops called limitanei) who were permanently deployed to the border and field army (comitatenses), which were strategic reserves kept further within the country to be moved from border to border as needed. The numbers of the army were increased to well over half a Million soldiers by introducing compulsory recruitment. Barbarians, of even whole units thereof, would also be drafted.
The fleet, on the other hand, had only a minor role in early Roman military. It was as late as 260 B.C.E, during the First Punic War, that first bigger fleet was created, to be further developed by Pompey the Great and Caesar. A permanent fleet was established during the rule of Octavian August. At a later time province fleets were established – (classis Pontica, classis Britannica) as well as river fleets on Rhine, Rhone, Danube and Euphrates. The navy was chiefly based at harbours of Misenum and Ravenna.
During the time of the Empire reinforcements were called supplementum. An aged soldier, who stayed with the legion after completing the mandatory duty was called emeritus. Men of 17 to 46 years of age, who could serve in the army, were iuniores.