Millennium 3D chess is a three-dimensional chess variant created by William L. D'Agostino in 2001 which employs three vertically stacked 8×8 boards, with each player controlling a standard set of chess pieces. The inventor describes his objective as "extending the traditional chess game into a multilevel environment without distorting the basic game."
Rules
Millennium 3D Chess rules extend the traditional chess game into a multi-level environment. For notion purposes, the three board levels are denoted 1, 2, and 3. Moves are recorded in the same manner as chess, using algebraic notation, with the only difference that each square is prefaced by its level number. The white and black armies begin, in standard formation, on boards 1 and 3 respectively. All pieces can always move as normal whilst staying on the same board. Additionally, every piece is able to move between boards. Each piece's additional permitted movement in the third dimension is extrapolated from its traditional movement as follows:
Kings can move one square up or down in addition to their regular movement.
Knights' L-shaped move can involve moving one or two steps up or down. As in standard chess, the knight is the only piece able to "jump" over other pieces.
Bishops can move up or down one or two boards, as long as it also moves the same number of squares in a diagonal direction.
Rooks can move vertically up and down while not moving in the other two dimensions. Additionally, a rook can move an equal number of squares vertically as it does in one of the lateral dimensions.
Pawns can move one square up or down whilst staying in the same position laterally, or they can advance one square and additionally move one board up or down. A pawn's first move can, optionally, be two squares vertically, or two squares forward and two squares vertically. Pawns can capture diagonally forwards on boards immediately above and below. En passant rules allow capture on the square passed through on a two-step first move, but a pawn cannot be captured en passant if its first move is two squares vertically only. Promotion requires the pawn to reach the opponent's back rank and starting board, i.e. white promotes at rank 8 of board 3, and black promotes at rank 1 of board 1.
