The fortress is an endgame drawing technique in which the side behind in material sets up a zone of protection around their king that cannot be penetrated by the opponent. An elementary fortress is a theoretically drawn (i.e. a book draw) position with reduced material in which a passive defense will maintain the draw. It is essential to be aware of these elementary, iron-clad fortress ideas, because often they can save you if you’re looking for them.
There are several common endings where basic impregnable “fortresses” allow for an iron clad draw, despite imbalances in material. One of the most common fortresses in chess is where the stronger side has a passed rook’s pawn, and the defending king need only control the queening square to secure the draw, because if the stronger side approaches the pawn, it will cause a stalemate, such as in the diagram below.
It is worth noting that the position is also a draw if the stronger side has the “wrong” color bishop, meaning the bishop which does not control the queening square, in this case a8, as in the diagram below.
Here, if the Bishop where the opposite color, then it would be a win for white, since he could evict the king from the corner and march forward with his pawn to the queening square. However, because the King is able to control the queening square without being harassed by the bishop, it is still an ironclad draw since stalemate occurs if the stronger king approaches.
Another common fortress is in endings of Bishop v.s Rook, without pawns. Here, if the defending king is able to get to the corner which is the opposite of the color from his bishop, then it is an ironclad fortress, as in the diagrammed position below.
Here, it is a draw because the bishop can interpose if the rook gives check, after which white must let up the pressure or it is stalemate. Obviously, this resource would not be available if either the king were stuck in the other corner, or if his bishop were the opposite color (which is two ways of saying the same thing, really.) So, in an ending of bishop v.s rook, the correct idea for the defending side is to race his king to a corner that is the opposite color of his bishop, while the stronger side should try to prevent this, or push the king into the corner the same color as the bishop, which would be a win. In practice, more often than not the position is drawn, except for where the king starts out stranded in the wrong quadrant.
Another common stalemate box is in the following diagram. After Black plays 1…Kb1 (although 1…Kc1 would also draw, since after 2. Kc3, threatening mate, Black’s under-promotion to a knight with check reaches yet another common endgame fortress), If then white follows with 2.Kb3 Ka1, 3. Rxb2 is stalemate.
Yet another common fortress, is where one side has lost a pawn race, but has a bishop’s pawn vs. the queen on an open board. An obvious prerequisite for this draw, however, is the position of the stronger side’s king. In the diagrammed position below, we have a critical position. With white to move, the position is a draw, since after f7, white will be threatening to queen, which forces black to give checks. When checked by the queen, the white king should not step in front of his pawn, since this yields a tempo to black and would allow for Black’s king to approach the pawn. Instead, Ka8! is the correct idea, and the pawn will remain immune from capture by the queen, since if Qxf7 with the King on a8, we have a common stalemate. HOWEVER, with white to move in this position, I am sad to say, it is a win. Earlier this afternoon I had a game featuring this critical position, in fact, I intentionally reduced to this ending thinking it was a theoretical draw. This is one of the things that Dan Heisman often talks about in his column “Novice Nook” over at chess cafe.com, how beginners have a bad tendency of quickly reducing into lost endings. In the game, I had the opportunity to keep the rooks on the board and fight it out, which would have been correct, however, armed with the knowledge that I could reduce to a “fortress” with my bishop’s pawn, I went ahead and exchanged off the rooks. I add this anecdote in here, because it is essential to understand that you need at least three spaces between your pawn and the opponents king if it is their turn, and two spaces if it is your turn, in order for this drawing resource to work.
An interesting example of this common drawing theme arose in the following Leko game, where he was able to save his shirt by using this stalemate theme.