Although the Romans did many other things besides fight battles, certainly one of their greatest achievements was the world's first really professional, paid army, whose soldiers conquered most of Europe and all around the edges of the Mediterranean Sea, and held on to it for five hundred years.
You can make Roman helmets, spears, and swords for your history museum or just as a project. The helmet on the upper right is made from a baseball cap spray-painted gold, some plywood, and broom bristles. The helmet on the left is made from a bike helmet covered with foil, some cardboard, and some yarn. The stand is an old lamp.
Below, there's a Roman shield made from cardboard and papier mache, dried and then painted. Some Roman shields were round like this one, but at other times Roman soldiers carried rectangular shields, so you could also make yours rectangular instead of round.
Or you could make a Roman sword, like the one below. This one is made from foam rubber, painted to look like metal.