The Crossrook slides like a bishop. It can make a capture by jumping over a piece of any colour. If an enemy piece is positioned immediately behind the jumped piece it will be captured (this is a "strong" Crossrook). But if the square behind the jumped piece is empty then the Crossrook can slide like a rook in the prolonged movement direction (two alternative directions). The strong Crossrook's value is 3, that is, the same as a bishop or knight. Otherwise the rules are the same as in standard chess, except for the possible promotion to Crossrook.
As the Crossrook loses 'screens' for jumping when the pieces become fewer, it is less valuable in the endgame than in the middlegame. In the middlegame it often appears to have a rook's value, but when the pieces are few it often becomes less valuable than a bishop. The Crossrooks can have a big positional influence from their initial position at the extra corner squares.
The 68-squared Gustavian board makes it possible to place additional pieces on the board without substantially increasing the board size. This often means that a strategical and tactical tension is maintained. It also brings the advantage that bishops and knights remain equal in value. Crossrook Chess, and the new Crossrook piece, were invented by undersigned, August 2006.
The Crossrook, slides like a bishop, but captures by a jump followed
by a rook's slide. Note that it cannot
capture the black knight because it
is not in the prolonged movement
direction. Had there been an enemy
piece at the position marked with a
green ring, it could have been captured
(as this is a "strong" Crossrook).