Portal:Chess/Selected article/Introduction/Fortress (chess)
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In chess, the fortress is an endgame drawing technique in which the side lagging in material sets up a zone of protection around their king that cannot be penetrated by the opponent. Clearly, it only works when the opponent does not have and cannot create a passed pawn, unless that pawn can be stopped (e.g. see the opposite colored bishops example). An elementary fortress is a theoretically drawn position with reduced material in which a passive defense will maintain the draw.
Fortresses are a problem for computer chess: computers are unable to reason about fortress-type positions except to the extent that their endgame tablebase allows.
