Scutum on Galerius Arch

[Flavivs Aetivs]

As far as I know, yes it was. The Oval Auxiliary shields (which were markedly different from Late Roman shields in that they were narrower and flat) were each called a Clipeus, while the Rectangular or semi-rectangular Legionary shields were called Scuta. However, it is known some Legions used the Clipeus too, and thought some Auxiliaries used the Scutum.