Most of the Roman arms and armor were basically copied from other cultures, mainly Greek in the early period and then Celtic (although Samnites, Umbrians and Etruscans also influenced it a lot, early on).
The chainmail ("It is believed that the Roman Republic first came into contact with mail fighting the Gauls in Cisalpine Gaul, now Northern Italy. The Roman army adopted the technology for their troops in the form of the lorica hamata which was used as a primary form of armour through the Imperial period".), the helmet ("In the Roman Republic, the Montefortino helmet was the first stage in the development of the galea, derived from Celtic helmet designs. Similar types are to be found in Spain, Gaul, and into northern Italy"), the gladius ("From the 3rd century BC, the Romans adopted swords similar to those used by the Celtiberians and others during the early part of the conquest of Hispania. This sword was known as the Gladius Hispaniensis, or "Hispanic Sword""). The Scutum shield afaik was developped independently and was uniquely Roman as was the Pilum, although most Celtic shields also used the iron bosse in the middle.
The La Tene celts were painted as barbarians and savages by the Romans in their histories, but they were a contemporary culture almost as rich technlogically.
In any case, good luck getting the devs to accept this, this has been asked for many times. I'd totally love having some Roman stuff to play around with.
But "Romans used crossbows"? Erm, really? Can I haz source? They used ballistae and torsion catapults, but crossbows?
