The rectangular scuta were constructed largely of strips of overlapping bentwood, possibly set in place by steaming over a curved form (in much the same way as a modern plywood chair is made) although no direct evidence survives to prove this. This meant the shield was strong and yet light enough to be carried over long distances. The best surviving example, from Dura-Europos in Syria, was 1.06 m (42in) in height, a chord of 0.66 m (26in), with a distance around the curve of 0.86 m (34in), and a thickness of 5 mm to 6 mm.

The curved shape of the shield allowed it to absorb (and deal) heavy blows, while the sides sloped away from the attacker, allowing arrows and enemy blows to glance off without transmitting the full force of the impact to the legionary sheltering behind it. The boss in the centre of the shield (the umbo), constructed either from copper alloy (brass or bronze) or iron, was itself used offensively, being heavy and dense enough to stun or wind an opponent (easing the legionnaire's subsequent strike with his gladius).