While the backbone of the Imperial Roman Army was their heavily armored Infantry Legions, the Romans also recognized the need for a professional mounted arm as well. Formed of regiments of non-Citizen Auxiliaries recruited from the provinces, these cavalry were professional soldiers paid by the Roman state.
Skilled in close-combat, these cavalrymen are also well protected. The thureos, a large oval-shaped shield, became common throughout the Hellenistic world from the 3rd century BC. Made from wood covered in hide, it differed from the earlier Greek hoplon in having a central handgrip, which was protected by a vertical spine running the length of the shield. This in turn could be further reinforced by the addition of a wide metal strip that protected the grip and the user’s hand. Inspired by the sub-rectangular and oval shields of the Celts, possibly through contact with the migrating Galatians, its usage seems to have spread through the Illyrian and Thracian tribes before it was adopted by the Greeks. Although large, the thureos was light in comparison to the traditional hoplon, and was adopted by heavily-armoured peltasts. Named after their shields, 'thureophoroi' could fight as common peltasts, skirmishing with javelins, but could also form up with their larger shields and longer spears in a similar fashion to a phalanx. The versatile and useful design of the thureos meant it was used by many armies, including the auxiliaries and cavalry of the later Roman Legions.