In Siege!, one player controls an army that is attacking a castle and trying to capture the other player's king. The other player is defending. Pieces in the turn are placed upside-down to hide their values. Each player has 10 pieces ranging in value from 1 to 4. The king is placed on a marked square on the far side of the board. Each turn, the players choose one piece and move it one square orthogonally (there is no diagonal) movement in the game. When a piece moves adjacent to an opponent piece, the values of both are revealed and the lower one is removed. There are also "trap" units which will automatically eliminate any unit they are adjacent to. The game ends when the defending king is captured or when the the invaders run our of pieces.