The most famous of the Roman shields, great scuta were large and either rectangular or oval. Early oval scuta evolved into the rectangular, semi-cylindrical versions, which were used by the foot soldiers of the early Empire to great effect. Their concave nature offered substantial protection, but made the use of weapons somewhat difficult as it restricted arm movement.
The use of rectangular scuta ended by the 3rd century AD, but scuta in general survived into the Byzantine Empire.
A battle formation that made excellent use of the great scuta was the testudo or tortoise formation, in which soldiers would gather close and align their shields both in front and on top. This protected the group from frontal attacks and projectiles launched from above.https://www.historyhit.com/kinds-of-ancient-roman-shields/Copied