Depends what period of Roman history. Swords were a major weapon for the late Republic, Principate and early Empire, but for most of the Empire's existence the primary weapon was the spear:The primary battlefield weapon for most ancient/medieval civilizations (Rome being the notable exception) were always spears I think
The spear was almost always the primary weapon in pre-gunpowder battles, because it was cheap, fairly easy to learn to an acceptable level, and a very effective killer.
The sword was a prestige weapon, and unlike a spear was easy to carry around without occupying your hands, but it was expensive and short range. Definitely a high-end side arm, not the primary weapon, in most armies.