Just to add something to your last sentence - I believe I read somewhere in Polybius that the Romans had never built a warship until the whole skirmish in Sicily kicked off the first Punic War, and they managed to do so by copying a Carthaginian vessel that had washed up ashore. They made one important improvement with an articulating walkway (I seem to remember it being called "the eagle" but I'm not sure) - they could swing it around and lock it to another ship to create a bridge for foot soldiers to attack.

Edit: It was called a raven or corvus: https://en.wikipedia.org/wiki/Corvus_(boarding_device)