Adrian Goldsworthy provides a good description of a Roman shield, called a scutum, in his book The Complete Roman Army on page 129. A well-preserved shield was found at Dura Europus that dates from the 3rd century.
The shield is 3’ 3” tall by 2’ 8” wide in a curved shape.
It is two inches thick, consisting of three layers of wood glued together.
The center layer is vertical and the two outside layers are perpendicular. On the inside there are strips of wood attached for extra strength. There is a thin layer of leather on the inside and outside. The edge has a wide leather binding and there are leather reinforcements on the corners.
There is an opening in the center of the shield for a boss (a hand grip), but one was apparently not attached. Instead there is a horizontal handgrip. I’m guessing that means there was a bar across the shield.
A reconstruction of this shield with a boss weighed in at 12 pounds.
The leather covering and wood core would have provided great protection against arrows, including flaming arrows.
Seems like the 2 inches of laminated wood have done a good job protecting from spears. Of course, if the spear penetrated you would likely have to drop the shield. If the spear stuck you would have to take precious seconds knocking it loose.
On a day-to-day basis, a scutum would be carried in a leather bag to provide protection to the shield.