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Roman Republic and early Empire

The cavalry in the early Roman Republic remained the preserve of the wealthy landed class known as the equites —men who could afford the expense of maintaining a horse in addition to arms and armor heavier than those of the common legions. Horses were provided by the Republic and could be withdrawn if neglected or misused, together with the status of being a cavalryman.

As the class grew to be more of a social elite instead of a functional property-based military grouping, the Romans began to employ Italian socii for filling the ranks of their cavalry. The weakness of Roman cavalry was demonstrated by Hannibal Barca during the Second Punic War where he used his superior mounted forces to win several battles. The most notable of these was the Battle of Cannae, where he inflicted a catastrophic defeat on the Romans. At about the same time the Romans began to recruit foreign auxiliary cavalry from among Gauls, Iberians, and Numidians, the last being highly valued as mounted skirmishers and scouts (see Numidian cavalry). Julius Caesar had a high opinion of his escort of Germanic mixed cavalry, giving rise to the Cohortes Equitatae. Early emperors maintained an ala of Batavian cavalry as their personal bodyguards until the unit was dismissed by Galba after the Batavian Rebellion.

For the most part, Roman cavalry during the early Republic functioned as an adjunct to the legionary infantry and formed only one-fifth of the standing force comprising a consular army. Except in times of major mobilisation about 1,800 horsemen were maintained, with three hundred attached to each legion. The relatively low ratio of horsemen to infantry does not mean that the utility of cavalry should be underestimated, as its strategic role in scouting, skirmishing, and outpost duties was crucial to the Romans' capability to conduct operations over long distances in hostile or unfamiliar territory. On some occasions Roman cavalry also proved its ability to strike a decisive tactical blow against a weakened or unprepared enemy, such as the final charge at the Battle of Aquilonia.

After defeats such as the Battle of Carrhae, the Romans learned the importance of large cavalry formations from the Parthians. At the same time heavy spears and shields modelled on those favoured by the horsemen of the Greek city-states were adopted to replace the lighter weaponry of early Rome. These improvements in tactics and equipment reflected those of a thousand years earlier when the first Iranians to reach the Iranian Plateau forced the Assyrians to undertake similar reform. Nonetheless, the Romans would continue to rely mainly on their heavy infantry supported by auxiliary cavalry.