Fortresses are not actually that common in the opening. It’s quite difficult to set up an adequate fortress at the start of the game. Nevertheless, there are some types of fortress structures that appear in the openings.
Diagram: Fortress setup for attacks
In the endgame, fortress setups are a drawing strategy. The goal is to block things up so completely so that your opponent cannot make any progress. Sometimes the word “fortress” is used to describe positions where a passed pawn is blocked, but really these are “blockade” not a “fortress”. A true fortress is where the position is so blocked that the attacking King cannot invade.
A fortress is also a swindling tactic. A fortress can create a draw even when your opponent is way ahead on material. Fortresses are especially good methods in Queen-vs-Rook endgames, which should be easily won for the Queen, but sometimes the Rook can create a fortress and draw. If it can be setup, the attacking King cannot come to support the Queen, and it’s drawn.
Diagram: Fortress in Queen vs Rook and Two Pawns
Diagram: Fortress Fails Because Passed Pawn with Queen
A fortress is more difficult to create with a Rook and only a single pawn. If the pawn can be defended by the Queen then the fortress will hold, and the Rook can move side-to-side. But in many such cases, the Queen can often get behind the pawn, and force the King away while doing so at a time that allows the attacking King to cross over behind the pawn. With both the King and Queen behind enemy lines the defender’s pawn will be lost, creating an elementary Queen-versus-Rook Endgame (which is itself quite excruciatingly difficult to actually win!).
Diagram: Fortress Does Not Hold
Related Chess Tactics
Read more about these related chess strategies: