Keeps are medieval cities surrounded by fortifying walls. The board to the cathedral game simulates a keep setting in that you build a city within the keeps walls. There are two sets of pieces, the light side and the dark side. These are opposing forces fighting for control over the city. The cathedral is a neutral portion of the city that prevents either side from having too much of an advantage over the other.

Play begins with placement of the cathedral, then players place buildings on the 10 x 10 grid board one piece at a time. The first player to place all his pieces while preventing their opponent from placing all of their pieces wins.

If in the process of placing a piece you completely surround another piece (and only one piece not of your color including the Cathedral), you may remove the surrounded piece from the board and the area thus enclosed is reserved for placement of your pieces only. Areas may be enclosed this way also if there are no pieces being surrounded.

Play ends when neither player may place anymore pieces.