Before Gaius Marius changed the Roman Army into a well-armed fighting machine, it was far less superior a force.  Each Roman soldier had to provide his own weapons and armor, they recieved no wage, and when the fighting was over they typically returned to their homes. Marius provided wages and weapons to every man entering the army, turning it ionto a more powerful force.

The Republic's Army is still a force to be reckoned with, avoid their Heavy Legionaire, he does some seious damage.