King

The king is the piece each player must protect, because the game ends when it is attacked and no permitted reply exists. That situation is called checkmate. Each side has one king. White's begins on e1, the square in vertical column e and horizontal row 1; Black's begins on e8, the same column in row 8.

Normally, the king moves one square in any direction and may capture an enemy piece on its destination. That destination cannot be attacked by the opponent. For the same reason, the two kings can never stand on adjacent squares, because each would attack the other. Castling is a special exception in which the king moves two squares and a rook also changes position.

When an enemy piece attacks the king, the king is in check. The player must make a legal move, meaning one permitted by all the rules, that removes the threat: move the king, capture the attacker, or, when a distant attack follows a horizontal row, vertical column, or diagonal with a square in between, place another piece in the way.

If no legal response exists, the position is checkmate. Any move that leaves one's own king attacked is an illegal move.