Chess80

Setup

Initial board setup. The Dukes are sitting at the left and right of the King and Queen.

Pieces

The Duke

The Duke is a leaper piece and can leap two squares in any direction. I can also move like an orthodox chess King however it is not royal (cannot be checked by other pieces). The Duke captures as it moves. Other fairy pieces that have the same movement are the Mastodon and the Squire.

In Algebraic notation, it is represented by the letter D.

NOTE: The triangles denote a jump; the circles a move to an adjacent square.

Rules

Generally speaking, aside from the Duke's movements and the expanded Castling rules below, Chess80 mechanics are idential in all aspects with those of Orthodox chess. This includes checking and checkmating, Pawn promotion (may also promote into a Duke), en-passant, 50-move limit and stalemate after threefold repetition.

Castling

Because of the wider board, and to allow for more King-Rook placement variability, castling in Chess80 is very similar to a concept called Flexible Castling first introduced by Fergus Duniho. In Flexible Castling, the King may move two or more squares towards the Rook, while the Rook leaps over to the square immediately on the other side. Additionally, in Chess80 the King is also allowed to occupy the corner squares of the Rook (see examples below).

Restrictions

1. Initial positions: Both the king and the rook involved in castling must be in their original starting positions (e.g. the king on e1 and the rook on a1 or j1 for white) and have not moved from those squares.
2. Empty path: All squares between the king and the rook must be empty.
3. Not in check: The king cannot be in Check at the time of castling.
4. Safe passage: The king cannot pass through or land on a square that is under Check by an ennemy piece.

King-Rook swap

The King may move two (2) or more squares towards the Rook (including the Rook square itself). The Rook is then leaped over to the square immediately behind the King. Castling notation is very similar to that of Orthodox Chess: King-side castling is annotated as N-N and Queen-side castling is annotated as N-N-N, where N represents the number of squares moved by the King. Note: in Orthodox Chess these are respecively written as 0-0 and 0-0-0.

Thus we can see below all possible variations:

• 2-2: King-side castle of two spaces
• 3-3: King-side castle of three spaces
• 4-4: King-side castle of four spaces (lands on the Rook square)
• 2-2-2: Queen-side castle of two spaces
• 3-3-3: Queen-side castle of three spaces
• 4-4-4: Queen-side castle of four spaces
• 5-5-5: Queen-side castle of four spaces (lands on the Rook square)

Example: 2-2 and 2-2-2 castling

Example: 3-3 and 3-3-3 castling

Example: 4-4-4 castling

Example: 4-4 and 5-5-5 castling (landing on the Rook square)

Notes

Design considerations

Movement

The initial consideration was to make the Duke color-bound like the FAD and thus provide a new piece that strikes a balance between the Knight and the Bishop, bringing the total number of leapers and color-bound pieces to two each. While this may seem more intuitive at first, it has some drawbacks:

1. Because of the larger board size, a minor piece like the FAD would not be as powerful and would lead to longer, more drawish games.
2. A King and a FAD cannot by themselves mate the opponent's King. Thus endgames need a 3rd helper piece other than the same-colored Bishop.
3. If there are two color-bound pieces (e.g. Bishop and FAD), there's a risk that both pieces of the same color are captured, thus leaving the player with a double disadvantage. While this could lead to a strategy on its own, it rarely produces a fun game.
4. The Queen and Rook are even stronger on a 8x10 board. The current version of the Duke is not colour-bound and controls 4 more squares, thus bringing it closer in power to these two pieces.
5. At the same time, we know from Capablanca chess (and other similar variants on a 8x10 board) that new pieces like the Archbishop and the Chancellor tend to overpower by the sheer number of squares they control, leading to imbalanced and complex games. These pieces are also complicated to grasp for novices, thus preventing wider adoption.

Board size

Given that Orthodox Chess is also played on a square board, why not use a 10x10 board which seems a more natural choice?

An 8x10 board has many advantages:

1. The overall proportion of pieces vs number of squares is preserved to exactly half. 32 pieces vs 64 squares for the orthodox chess and 40 pieces vs 80 squares for the 8x10 board.
2. The 10x10 board leads to longer games and tends to delay initial confrontation.
3. Some pieces like the Knight become weakened.
4. Fits rather well on a smartphone in landscape mode

Defensive coverage of the Pawn rank

Chess80 has been designed to provide a symmetrical protective barrier of the Pawn rank and prevent unbalanced weaknesses which could give the enemy additional advantage. The numbers indicate the amount of protection each Pawn receives from the major pieces behind.

Defensive coverage of the 3rd rank

The rank immediately facing the Pawn line is equally important. The defensive formation below is kept constant except for the edge files.

Controlling squares and relative value of pieces

Below figures are estimates and take into account the larger 8x10 board.

Some things to keep in mind:

1. The Knight is slightly less powerful as it needs more lateral movements to go from one side of the board to the other.
2. The Bishop has the exact same strength as in orthodox Chess since diagonals remain the same.
3. The Queen and the Rook have slightly more reach on a 8x10 board because of the increased files.
4. The Duke's value should be higher than a Rook's because it can leap (can't easily be boxed-in), placing it somewhere in between the Rook and the Queen.

Last revised by Alex Damian.