The ability to conscript crews gave rulers the ability to put a fleet at sea quickly. The Greeks were able to rush a fleet to sea when threatened by the Persians, as were the Romans in their war with Carthage. Creating fleets was a function of shipbuilding, assembling crews, and training. Oar-powered ships required only a few skilled sailors, but a hardy crew of fit and motivated men on the rowing benches could mean the difference between victory or defeat. Slaves, in general, made for poor rowers.