Check out Chess with Different Armies, our featured variant for July, 2024.

This page is written by the game's inventor, Charles Gilman.


When I created my first 3d variant, Tunnelchess, I soon became aware of the need for a considerably stronger army on a 3d board than merely proportional to board size relative to FIDE Chess. This led to the Intermediate and Pawnless variants of Tunnelchess, still on the 4x4x8 board. Eventually I devised a distinct family of variants on a different shaped board - 6x6x6 to allow 36 pieces at each end with a Pawn (or similar) in front of each piece. These were Unionschach, Sachsenschach, and Leapale. Meanwhile I had already devised a 4-player variant on such a board, Grossraumschach, but now felt that this suffered from the same lack of strength as Simple Tunnelchess. Then I thought of four recessed camps with a small central empty area, in the style of Fivequarters. CROSSTUNNEL is designed as a 4-player version of Intermediate Tunnelchess, using two pairs of camps but sharing the cube of empty cells in between and so doubling piece numbers while increasing the cells by only 50%. Additionally we shall see that pieces can change sides to build up surviving armies to fight to the end. It is paradoxical that having used the same board as Grossraumschach to improve on Tunnelchess as a 2-player variant I should use a derivative of the Tunnelchess board to improve on Grossraumschach as a 4-player one!


As the board has so many cells and four piece colours, rather than show piece images and individual cells I will show letters each representing two 2x2x2 "supercubes" one above the other. The Levels are from a at the top to d at the bottom, and each supercube letter represents cells on all four levels. Leftranks are numbered from 1 (Red first rank) to 8 (Green first rank) and Rightranks from 1 (Blue first rank) to 8 (Orange first rank). Leftranks intersect with Levels to form Rightfiles (1a-8d), Levels with Rightranks to form Leftfiles (a1-d8), and Leftranks with Rightranks to form Ranklings (13 - meaning Leftrank 1, Rightrank 3 - and 31 - meaning Leftrank 3, Rightrank 1 - to 68 and 86). Cells are represented by the Rankling number with the Level letter in the middle.
R=Red camp, ranklings 13-16 outer, 23-26 inner
O=Orange camp, ranklings 38-68 outer, 37-67 inner
G=Green camp, ranklings 83-86 outer, 73-76 inner
B=Blue camp, ranklings 31-61 outer, 32-62 inner
C=Common central third, ranklings 33-66
_=absence of ranklings


The QUEEN is the one FIDE first-rank piece in this variant, moving any distance on the orthogonal or the standard diagonal but not the nonstandard one (commonly known as triagonal). There are four Queens aside, starting on the cells:
Red 1b3 1b6 1c3 1c6
Orange 3b8 3c8 6b8 6c8
Green 8b3 8b6 8c3 8c6
Blue 3b1 3c1 6b1 6c1

The DUCHESS moves any distance on the orthogonal or the nonstandard diagonal but not the standard one. There are four Duchesses aside, starting on the cells:
Red 1a4 1a5 1d4 1d5
Orange 4a8 4d8 5a8 5d8
Green 8a4 8a5 8d4 8d5
Blue 4a1 4d1 5a1 5d1

The GOVERNOR moves any distance on either kind of diagonal but not the orthogonal. There are four Governors aside, starting on the cells:
Red 1a3 1a6 1d3 1d6
Orange 3a8 3d8 6a8 6d8
Green 8a3 8a5 8d3 8d6
Blue 3a1 3d1 6a1 6d1

The EMPRESS moves any distance in any radial direction. There are two Empresses aside, starting on the cells:
Red 1b4 1c5
Orange 4c8 5b8
Green 8b5 8c4
Blue 4b1 5c1

The EMPEROR moves one cell in any radial direction. There are two Emperors aside, both needing to be kept out of check, and starting on the cells:
Red 1b5 1c4
Orange 4b8 5c8
Green 8b4 8c5
Blue 4c1 5b1

If you are using distinguishable sets and wish to be adventurous, you could try one type of Pawnlike piece on the Frame and Tunnel, and another on the Wall. My article Man and Beast 2: Shield Bearers lists some to choose from. The most obvious combinations are Pawn and Yeoman, Broker and Lowlander, and Warder and Highlander. Whichever you choose, they have an optional initial double-step noncapturing move and En Passant. They start on the following cells:
Red throughout Leftrank 2
Orange throughout Rightrank 7
Green throughout Leftrank 7
Blue throughout Rightrank 2


Play proceeds in anticlockwise order starting with Red. As this variant is both 3d and 4-player it will be no surprise to those who know my variants that there is no Castling!

Moves from one camp to another must pass through a cell in the centre third. Thus 1a5-2a4-3a3-4a2-5a2 is a valid Bishop move (assuming no intervening pieces) but 1a4-2a3-3a2-4a1 is not. Likewise 1a5-2b4-3c3-4d2 is a valid Unicorn move (again assuming no intervening pieces) but 1a4-2b3-3c2-4d1 is not.

Second-rank pieces reaching another player's first rank or the intersection of the opposite player's third rank and an adjacent player's second rank must be promoted. For example, Red's promotion zone comprises ranklings 31-61-62, 38-68-67, and 83-86. I imagine that promotion will usualy be to Empress, although presumably underpromotion will very occasionally be useful. For example Red might want Orange to escape checkmate by Green by a move exposing Blue to checkmate by Red.

As an alternative to a normal move, a player can reintroduce a piece captured from an opponent, preserving any promotion.

A player one of whose Emperors is en prise to the player about to move is Checkmated. The Checkmated player's Emperors are removed from the board and the rest of their army taken over by the player about to move. This is why one player might want prevent Checkmate of another by a third. That player then makes their move and has the choice of moving a piece that they already had, moving a newly acquired one, or reintroducing a captured piece.


As pieces are likely to change hands a lot (to maintain total power), there is little point painting Staunton sets in the four colours. It is better to use coloured markers that can easily be removed and replaced as required. These could be string tied on, plasticene stuck on, or caps/collars/cloaks of coloured card. An alternative would be to use directionalised novelty (or even Shogi!) sets and face them in the relevant direction. Four FIDE sets will fill the array, but you may want spares for promotion. Four Shogi sets will be more than adequate for all purposes (three are not quite enough). In each case players must remember the "new" meanings of the piece representations.

In theory there could be a 6-player Crosstunnel with (say) Yellow and Purple camps above and below the central area, but that would be a lot more complex. The levels would be ranks for the two new armies, and the Ranklings for the four old ones would be the new ones' files. Also two of the existing armies would need rotating for a consistent relationship between all adjoining pairs of players and the new players could not sit "behind" their camps. All in all I consider four players quite enough.

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By Charles Gilman.
Web page created: 2006-01-21. Web page last updated: 2018-07-15