Defined as service to the ''Senatus Populusque Romanus'' - an agency designated by 'SPQR' on public inscriptions
Stretched over 1300 years and saw Roman armies campaigning as far east as Parthia (modern-day Iran), as far south as Africa (modern-day Tunisia) and Aegyptus (modern-day Egypt) and as far north as Britannia (modern-day England, south Scotland, and Wales)
Initially, Rome's military consisted of an annual citizen levy performing military service as part of their duty to the state
During this period, the Roman army would prosecute seasonal campaigns against largely local adversaries
Military service in the later empire continued to be salaried yearly and professionally for Rome's regular troops
Trend of employing allied or mercenary troops was expanded such that these troops came to represent a substantial proportion of Rome's forces
Roman troops were armed after Greek and Etruscan models, using large oval shields and long pikes