The Scutum is a shield carried by Roman soldiers. The Roman Centurion is shown carrying it, though it was not listed as one of his offensive weapons but it was tested in at least one test, it is shown being tested in the Aara test as part of the Centurion's armor set.
The Scutum (Latin for "shield") is a rectangular, semi-cylindrical shield about four feet in height and two-and-a-half feet wide.
The Scutum was as important to the Roman legion as the Aspis was to the Greek phalanx. Its large size and shape allowed soldiers to form sheild walls. Even in one-on-one combat, the Scutum provided it's user with excellent all-around protection. In the show, a demonstration of how the Scutum shield was used in combination with the Gladius sword for offensive purposes was shown in the show, although the shield's use wasn't taken into account.
In addition to Roman soldiers, the Scutum was carried by the Murmillo-class of Gladiator.
The modern riot-control and SWAT shield resembles a Scutum as both are designed to work in large formations for almost full frontal protection.