The game takes place over a number of rounds, each composed of three phases.
In the Battle phase, a.k.a. "Prepare for Battle," players use a crosshair to aim cannons at enemy ships, or the walls of the other player forts in multiplayer. The action is similar to Atari's earlier hit Missile Command. During this time, incoming cannonballs attack and destroy some of the walls around each player's castles. After about ten seconds of combat, the game announces a cease-fire, and then moves on to the Building phase.
In the Building phase, a.k.a. "Build & Repair," players are given random building pieces to attempt to rebuild their damaged walls. Pieces may be moved freely around the player's landscape, but can only be set down in a location where there is nothing blocking it. Bigger pieces can cover more ground, but are much harder to set down in a spot where they aren't blocked.
The Building phase is timed, and players get as many pieces as they can place during this time. If at least one castle is completely surrounded before time expires, the game plays a fanfare, different for each army. Diagonal gaps in walls do not count for surrounding castles. After time runs out, players who fail to surround a castle are knocked out of the game, although they may continue a limited number of times by putting more money in the machine.
In the Cannon phase, a.k.a. "Place Cannons," players receive a number of cannons according to the number of castles they captured in the Building phase. Having control of the player's initial "Home" Castle awards two cannons, and any other castles grant one cannon each. These cannons may be placed inside a player's walls in any empty 2x2 space. Having more cannons allows a player to get off more shots during later Battle phases, but cannons only work during a battle if they are also within walls. Once placed, cannons cannot be removed unless the player loses and continues, and if too many are built it becomes harder to complete walls during the Building phase. Players can signal that they are done placing cannons early by making five rapid illegal placements.
When playing alone, the player faces a series of six levels of increasing difficulty. The player may choose the order in which they play the first four levels. But first, they are given an option to play on Recruit or Veteran difficulty. Starting on Veteran begins play on level 2, and grants 5,000 bonus points. If playing on Veteran, one of the first four maps goes unselected. Level 5 takes place on a choice of two peninsulas, and only have three castles as options to capture. If the player can make it to Level 6, they must survive a ruthless onslaught on a small island with a lake on it, and only two castles. Completing this level wins the game, but very few players are capable of this feat.
If a player cannot capture a castle in time, they lose, and must spend money to continue playing. The player can only do this up to four times. There is an exception to this: if a player manages to reach the final level when they're on their last continue, the game will allow them one extra continue--although in that case, it will also downgrade their cannons by one step at the start of the lest level. (See: Continuing and Firepower)
During single-player Battle phases, the player's walls are shot at by the ships of an enemy armada gathering in the water off-shore. To win the map, a sufficient number of ships must be destroyed, and the enemy's numbers surviving on the level must be below a certain amount. (Grunts are counted among the surviving enemy for this purpose.) A maximum of 16 ships can be on-screen at once. So long as the player can capture at least once castle every Building phase, a map can continue indefinitely.
As the game continues, three kinds of enemy ships join in the attack:
Single-Sailed Ships must be hit by two cannonballs before they sink. The weakest ship, they have no other abilities.
Double-Sailed Ships are landers. They require three hits before they are destroyed. They have the same firepower as Single-Sailed Ships, but during battle they try to maneuver close to land. If one of them manages to reach a diagonal section of shore, then during the following Building phase they drop off Grunts.
Red Ships are command ships. They must be hit five times to destroy them. They do not leave Grunts, but their cannonballs, when they strike a wall, leave a flaming crater behind. Craters cannot be built upon, and persist for either two or three rounds, depending on how recently the player has continued the game.
Starting with level 4, these ships are replaced by darker versions of each type. These ships require an extra hit to sink.
During battle, ships often move around, and they seem sometimes to dodge out of the way of your shots. Ships that are closer have less chance to evade your fire, you can get more shots in on them in time, and if they're landers you might be able to sink them before they drop off ground troops. But ships further away tend to be in a crowd with other ships, and have less avenue for escape.
The Grunts left by the landers are the only enemy that can move around during the Building phase. They progress towards the nearest castle, and slowly increase in number as they travel. They usually move orthogonality, but can sometimes slip through diagonal gaps in walls. Walls cannot be set down on top of a Grunt. If the player manages to surround any Grunts with walls they are destroyed, with a satisfying "crunch" noise. Grunts tend to form large blobs that make it difficult, or even impossible, to capture castles. Grunts that survive into a Battle phase can be shot with cannons. At a random time during every Battle, each Grunt will destroy a wall or castle they're pointing towards. This is the only way a castle can be destroyed in play.
Pieces are selected from a "bag" of possible choices. At the start of a map, small and simple pieces are in the bag. As more pieces are placed, they become larger and more complex. Pieces can be moved and rotated freely before they are placed. When time expires (its ending is heralded by a series of more and more insistent snare drum beats), each player is given about four extra seconds to place their last piece.
The biggest problem with building walls is congestion, when the ships leave a mess of blocks it's difficult to build around. If the wall is near a barrier like the water or the edge of the screen, it is easy for them to make holes that are hard to fill. Experienced players learn to pick castles away from the edges, although, if they're far from the water, this makes it harder to hit enemy ships in battle.
The most flexible piece is the 1x1 square, which can be set in the most places, but these become very rare later in the game. A general rule about Rampart is, it's easier, and faster, to build new walls than to repair old ones. If you have a lot of space around a swiss-cheesed wall, it can be more viable to just surround the whole thing, castle, rubble, and all. This strategy becomes very difficult to use in levels 5 and 6.
A little-known fact about arcade Rampart is that ships tend to hit walls on the outside of your territory in preference to interior walls. It is possible, if they run out of targets (say, if there are many nearby ships or few walls), for them to hit walls further in, but often, if you can build a double wall around a castle, it'll emerge unscathed from the following battle.
If Grunts manage to get dropped off onto your domain, they are a dire threat. Double-Sailed Ships that may land should be a high priority for your shots. Remember: they can only land on diagonal shores! There is one exception: on Level 5, ships in the small area in the upper corner of the screen can leave Grunts if they reach the place where the land touches the edge of the screen!
Grunts can destroy castles, and make it impossible to capture castles they surround. You can place pieces in their path to mitigate their approach, but they are smart enough to go around, if there's room. They can sometimes even slip through diagonal gaps. If you have a grunt infestation, it is worth it to try to destroy them with cannonballs during the Battle phase. Note that it is difficult to hit Grunts that are behind walls or castles. A Grunt revealed by the destruction of an obscuring wall will be discolored, but will still be active during the next Building phase if you don't destroy it!
Surrounding Grunts with walls to destroy them is difficult and time consuming, but very satisfying to pull off.
Players get two cannons each round for having their home castle, one for each other castle. Cannons placed adjacent to a castle form a unit with it, and from then on must be captured together. It's easy to end up with a large mass of cannons around a castle, making it very hard to capture. Placing cannons further away is safer, but since cannons can only be placed inside walls to begin with, it can be difficult to set up.
Be especially wary about a castle/cannon blob getting too close to the water or screen edge. If a cannon gets placed one space away from either, it is very easy to get into a situation where only one or more 1x1 pieces can save that castle. Even worse, these situations are vulnerable to the shots from Red Ships. A crater takes two or three turns to disappear. If you can trace a line of craters from the water or screen edge to a castle, that castle is impossible to rescue until some of the craters go away. It is possible for a map to become completely unwinnable in this manner.
Continuing and Firepower
If you fail to capture a castle in a Building phase, you are knocked out of the game, but can pay to continue the game up to four times (possibly a fifth on the last level). When you continue, any cannons, ships, walls, grunts and craters are removed from the level, any destroyed castles are replaced, and you must start from scratch, from selecting a new Home Castle.
When you are offered the chance to continue, the game says it's "with MORE FIREPOWER." After a continue, you get four cannons to place at the start of the level, rather than the usual two. But more importantly than that, the cannons you place are actually more powerful. The first two times you continue, their shots travel faster, which both lets you get off more shots in battle and hit ships more easily. These upgraded cannons look different. The next two times you continue after that, your shots become stronger. On credit #4, all ships take one fewer hit to sink, and on credit #5 (usually your last chance), ships take two fewer shots to sink. It is extremely difficult to win at Rampart, even on Easy machine settings, without this advantage. If you make it to the final level with fully upgraded cannons, the game gives you another continue, but also downgrades your cannons to the previous level! To get your upgrade back, you have to continue another time.
Up to three people can participate in a battle against each other. The screen is divided into a number of areas, separated by rivers, and each player is given ownership of one of these areas of land. Instead of firing at ships and grunts, the player's targets are the walls around the other armies' castles and their cannons themselves. By shooting walls, players can make it harder for the others to capture a castle. Each cannon can take a limited number of hits until it turns into a useless pile of immovable rubble. This usually surprises players the first time they discover it's possible. In most home ports of Rampart, the ability to destroy cannons can be turned off.
If a player fails to capture a castle, they are knocked out unless they spend money to continue playing. This improves their cannons by one step, letting them get more shots off in Battle phases. Each player may only continue twice before being eliminated for good.
If a player chooses not to fire during a Battle phase, their cannons will select their own targets. This can be an effective way to do battle, as their cannons tend to choose random, far-flung targets, leaving holes that are harder to repair.
After a number of rounds (the exact number is adjustable by the operator), if no winner has been decided, the game will declare it to be the Final Battle at the beginning of a Battle phase. If more than one player survives the subsequent Building round, the winner of the game is determined among survivors by whoever has the highest score. If no player survives during Final Battle, the game is known to sometimes grant them an additional building phase, or maybe even two, before declaring everyone's game to be over.
In the arcade version of Rampart, a winning player can behead the losers in a victory scene after the game. If the winner doesn't touch the control for a few seconds, they will "spare" the loser.
A little-seen variation on multiplayer Rampart can be seen if two players opt to play again at the conclusion of a game. The players will be given a choice between a standard two-player map, or a special map with less land to build on and an ocean area containing player-controlled ships. These ships can be sunk by enemy cannonballs, and fire at enemy walls of their own accord.
If the winner of a multiplayer game continues into a new multiplayer game, then as a handicap, they will receive one fewer castle at the start. If you wish to avoid this, from the lobby screen, let all of the player stations' timers expire before beginning the next game. (This will reset everyone's score totals, unfortunately.)