The black board includes a perimeter troth just a tad shy of being able to hold all 30 balls comfortably it can be done, but you have to position things just so. The center of the board features a 4x4 grid of ball-sized depressions.
Players take turns placing one of their balls onto the board.
Once four balls form a 2x2 square, it becomes possible to place a ball on top of them in the center of the square. When this is possible, instead of playing a marble from off the board a player may elevate an already-placed ball to a higher level provided no balls are already on top of the one being moved. If a player forms a 2x2 square of marbles all of his color, he may immediately remove up to two of his marbles from the board. The removed marbles can't have any other marbles on top of them, but can include the marble just placed. We've found that this rule makes the game much more interesting and highly recommend it.