I'm coming along with my fantasy novel (original, I know). I would compare my world closer to the gladiator times than medieval but that's another issue. I have a battle scene between two kingdoms that I am really proud of, except for one missing element. Basically the defending kingdom is located on the coast with a bay leading into the heart of city. The attacking kingdom attacks (redundant) the city by surprise and is able to get naval ships into the bay. As the attacking navy gets closer to the city, the defending city uses an advanced weapon to take down the ships and force a retreat. What could this weapon possibly be? I have come up with ideas but I'm not exactly satisfied with them. I'm not convinced they would even work. One idea was as the ships get closer to the coast, hatches open from the towers and boulders roll out onto the ships, sinking them (UGH). My other idea was a catapult type thing but instead of rocks or boulders, using a flammable liquid to where a flaming arrow could like the ships on fire (also ugh). I would rather not shy away from using the "advanced" weapon. It furthers the plot for me as the weapon is not something the attacking city has ever seen. They discover a third kingdom shared the technology with the defending kingdom, and retaliate. I haven't described the plot into detail and am not looking for critiques on it. Just looking for help with the weapon. Any ideas are greatly appreciated. Thank you.