Quotation from: The Chessmen of Mars

Written by: Edgar Rice Burroughs

When a player, moving properly and in order, places one of his
pieces upon a square occupied by an opponent piece, the opponent
piece is considered to have been killed and is removed from the
game.

The moves explained. Straight moves mean due north, south, east,
or west; diagonal moves mean northeast, southeast, southwest, or
northwest. A Dwar might move straight north three spaces, or
north one space and east two spaces, or any similar combination
of straight moves, so long as he did not cross the same square
twice in a single move. This example explains combination moves.