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Circular chess

Circular chess is a chess variant played using the standard set of pieces on a circular board consisting of four rings, each of sixteen squares. This is topologically equivalent to playing on the surface of a cylinder.

Documents in the British Library and elsewhere suggest that circular chess was played in Persia as early as the 10th century AD, and further references are found in India and, later, Europe. The rules then used do not survive, so when, in 1983, Lincoln historian David Reynolds came across a reference to the game being played in the Middle Ages and set about attempting to revive interest in it, a new set of rules had to be drawn up, based around those of square chess. The starting position is essentially obtained from that of square chess by cutting the board in half and bending the two halves to join at the ends. Two lines are marked on opposite sides of the board, and each set of pieces is positioned so as to straddle this line. The king and queen start on the innermost ring, with, as is the case in square chess, the queen on a square of the same colour; the bishops start in the second ring from the centre, the knights on the third and the rooks on the outermost ring. The pawns are positioned in front of the pieces.

The moves of the pieces are identical to those in square chess; a queen or rook may, if it is not obstructed, move any distance round a ring, except that the "null move" of moving a piece all the way round the board and back to its original square is not permitted. A pawn is promoted after moving six squares from its initial position, to the square immediately before the opponent's starting line. Castling and en passant captures are not permitted. Announcing a check is not obligatory, and "snaffling" (winning the game immediately by capturing the opponent's king after he either moved into or failed to move out of check) is allowed - and has on more than one occasion decided a world championship game.

Most textbooks on square chess assign the pieces relative values of 9 points for a queen, 5 for a rook, 3 for a bishop or knight, and 1 for a pawn; although no attempt has been made to assign specific values for circular chess, it is certain that the same values do not hold. The values of the queen and rook are considerably augmented by their greater range - with two rooks or a queen and rook unobstructed on the same ring being especially powerful - while those of the bishop and knight are diminished; for example, on a square board two minor pieces are held to be stronger than a rook, but on a circular board the rook is considerably stronger. The minor pieces do, however, pose a significant danger value, as their moves are more difficult to visualise on the circular board and even strong players often fail to notice a threat.

One of the major differences between square and circular chess in practice is in the opening. In the former, opening theory has developed over several centuries, and the use of computer analysis has resulted in top level games frequently not deviating from known theory until the 20th move or beyond; in the latter, there is virtually no opening theory, and consequently players are "on their own" from the first move. In square chess, advancing the king's or queen's pawn are generally considered the best opening moves, as doing so attacks two key central squares, opens a diagonal to enable the development of a bishop, and, in the case of the king's pawn, the queen also. On a circular board these advantages are negated, as a king's or queen's pawn only attacks one square, and its advance only opens one square for the bishop. Some players advance the central pawns first anyway, while others prefer to advance the rooks' pawns in order to open lines of attack for the more powerful pieces; it is not known which move, if any, is objectively best.

The different geometry of the square and circular boards creates considerable differences in endgame theory: three of the four "basic mates" on a square board (those with king and rook, king and two bishops or king, bishop and knight against a lone king) rely on forcing the defending king into the corner of the board, and thus are impossible on a circular board since it doesn't have corners. The "basic mates" in circular chess are thus those with king and queen, king, rook and minor piece or king and three minor pieces against a lone king. The greater tendency towards drawn endgames often results in the defender playing on in a position which would be considered cause for resignation on a square board. In one particular endgame, however, the circular board favours the attacker: with king and pawn against king, there is no stalemate defence and thus, unless the defending king can capture the pawn before it can be either promoted or defended, this endgame is always a win.

The Circular Chess Society