The Roman army (; Ancient Greek: ) is the generic term for the terrestrial armed forces deployed by the kingdom of Rome (to ca. 500 BC), the Roman Republic (500-31 BC), the Roman Empire (31 BC - AD 476) and its successor, the Byzantine empire (476-1453). It is thus a term that spans approximately 2,000 years, during which the Roman armed forces underwent numerous permutations in composition, organization, equipment and tactics, while conserving a core of lasting traditions.
The development of the Roman army may be divided into the following 8 historical phases:
The Early Roman army of the Roman kingdom and of the early Republic (to ca. 300 BC). During this period, when warfare chiefly consisted of small-scale plundering-raids, it has been suggested that the Roman army followed Etruscan or Greek models of organization and equipment. The early Roman army was based on an annual levy or conscription of citizens for a single campaigning-season, hence the term legion for the basic Roman military unit (derived from legere, "to levy").
The Roman army of the mid-Republic (a.k.a. as the "manipular army" or the "Polybian army" after the Greek historian Polybius, who provides the most detailed extant description of this phase) of the mid-Republican period (ca. 300-107 BC). During this period, the Romans, while maintaining the levy system, adopted the Samnitemanipular organization for their legions and also bound all the other......