Early Roman army

The Early Roman army was deployed by ancient Rome during its Regal Era and into the early Republic around 300 BC, when the so-called "Polybian" or manipular legion was introduced.

Until c. 550 BC, there was probably no "national" Roman army, but a series of clan-based war-bands, which only coalesced into a united force in periods of serious external threat. Around 550 BC, during the period conventionally known as the rule of king Servius Tullius, it appears that a universal levy of eligible adult male citizens was instituted. This development apparently coincided with the introduction of heavy armour for most of the infantry.

The early Roman army was based on a compulsory levy from adult male citizens that was held at the start of each campaigning season, in those years that war was declared. There were probably no standing or professional forces. During the Regal Era (to c. 500 BC), the standard levy was probably of 9,000 men, consisting of 6,000 heavily armed infantry (probably Greek-style hoplites), plus 2,400 light-armed infantry (rorarii, later called velites) and 600 light cavalry (equites celeres). When the kings were replaced by two annually-elected Consuls in c. 500 BC, the standard levy remained of the same size, but was now divided equally between the Consuls, each commanding one legion of 4,500 men.

It is likely that the hoplite element was deployed in a Greek-style phalanx formation in large set-piece battles. However, these were relatively rare, with most fighting consisting of small-scale border-raids and skirmishing. In these, the Romans would fight in their basic tactical unit, the centuria of 100 men. In addition, clan-based forces remained in existence until at least c. 450 BC, although they would operate under the Consuls' authority, at least nominally.

In 493 BC, shortly after the establishment of the Roman Republic, Rome concluded a perpetual treaty of military alliance (the foedus Cassianum), with the combined other Latin city-states. The treaty, probably motivated by the need for the Latins to deploy a united defence against incursions by neighbouring hill-tribes, provided for each party to provide an equal force for campaigns under unified command. It remained in force until 358 BC.

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