Explanation: In the First Punic War, the Roman Republic began the war without a navy - while Carthage (the Punics) was the premier naval power in the world. A number of weird Roman things occurred - like the Romans finding a single mostly-intact wreck of a Carthaginian ship and using it as a template to make a 200-ship fleet with - and then losing that fleet and building another, and then a third - but one of the more fascinating aspects was the creation of the corvus.
Romans, as they had not been on the seas long, were kind of dogshit at naval combat. Their rowers (free men, contrary to depictions of galley rowers as slaves) and crew simply did not have the experience to meet the Carthaginian fleets' maneuverability, making the Romans vulnerable to ramming and bombardment with missiles. Boarding existed as a tactic, but specialized marines were needed, men with light equipment and their sea legs, so they wouldn't fall into the drink and drown horribly when trying to cross over on a narrow boarding plank to a ship filled with people trying to make sure no one crosses over. So what was the Roman solution?
The corvus. Named as such because it resembled a raven's beak, the corvus was a huge, heavy bridge with a big-ass iron spike at the end. Suspended on a ship, it could be rotated and dropped into any enemy ship that drew too close, the spike jamming itself into the enemy's deck and lodging the bridge in place. Instead of needing men with sea legs to cross a narrow board, the Romans now had a nice, sturdy bridge with only a small chance of falling off and drowning; the kind of thing a bunch of landlubbers could use. So the Romans then loaded up some experienced troops, with big, heavy shields and heavy armor, and promptly obliterated the Carthaginians in several battles - because they could simply charge across.
The corvus eventually fell out of use because having a huge bridge hanging off of your ship is a great way to capsize in rough weather. But it served its purpose - it bought the Romans enough time to learn the traditional way of naval warfare!
