Rampart

Rampart is an arcade action/strategy/puzzle game originally made for arcades, and which got widely ported. It was fairly popular for its time, getting rave reviews in a number of magazines. It has a very difficult single-player mode, but most people enjoyed it for its multiplayer mode, which in arcades supported up to three players.

Gameplay
Players are put in command of either the Blue Army, the Red Army, or the Orange Army, and tasked to guard their shores from invaders. In the single-player mode, these are enemy ships and ground units coming in over the ocean. In multiplayer, these are the other players, fought from across the banks of a river. Each army has a section of landscape, dotted with castles. At the start of play, they are given an initial wall around a castle of their choosing. During the game, this wall is damaged by incoming cannon fire, and must be rebuilt in order to stay in the game. It doesn't have to be built exactly as it was before. So long as there is a continuous wall around at least one of the player's castles, they get to go on. More than one castle can be captured at a time, which increases the rate at which a player amasses firepower.