CCLA Server Chess

The Bishops of Opposite Color Fortress

One of the most interesting aspects of the bishops of opposite color (BOC) endgame is a special arrangement of kings, bishops and pawns known as the fortress. Before we begin the discussion of the technical details of the fortress, let’s examine an exceptionally instructive example to get a feel for what this type of position looks like.

This is diagram No. 52, page 28 of Ray Cheng’s excellent book, Practical Chess Exercises, 600 Lessons from Tactics to Strategy². At first glance this position looks hopeless for Black. Black is down two pawns, the passer on f3 does not appear to have a future and White’s connected passers on g5 and h5 look decisive. Watch the position change into a fortress and become hopelessly drawn. Cheng gives “1. ... f2!! clears the f3 square for the bishop. 2. Bxf2 Bf3 3. h6 Kg6. Black has successfully blockaded the enemy passed pawns, ensuring a draw.” After we study the elements of a fortress, we will return to this position and discuss how this particular fortress works. We will begin with three of the most important elements.

The first main element of a BOC fortress ending is, of course, the BOCs themselves. Moving on opposite colors, they cannot interact with each other and this has significant consequences, namely in generating a lot of draws. In practice this means the inferior side has an extra piece for defense. Sometimes even if the stronger side has one, two or even three more pawns, the game may still turn out to be a draw. It is important to remember that not all BOC endings are drawn as the superior side can have an effective extra piece to participate in an attack.

The second element of a BOC ending is the color relationship of the bishops with the pawns on the board. Mueller and Lamprecht provide some rules for this relationship on page 118 of Fundamental Chess Endings⁴. The authors note that this advice is somewhat different from earlier rules for same-colored bishops.

      “Rule 1: the defender should place his pawns on his own bishop’s color and force the attacker’s pawns to the opposite color.”

      “Rule 2: the attacker should, as always, place his pawns on the opposite color to his own bishop.”

The third element of a BOC ending is determining the proper color and location of the square for the defending king. To illustrate how these elements play out on the board we will look at two positions from Lasker’s Manual of Chess³.

This is diagram No. 2 from page 232 of Lasker’s Manual of Chess³. Lasker gives “Black cannot win since he is unable to advance either of his pawns. For instance, 1. ... Kd4 2. Kb2 Ke3 3. Kc1 Ke4 4. Ba5 Kd5 5. Kb2 Kc5 6. Ka3. The bishop on h5 is wholly inactive, the pawns have been deprived of useful work. The bishop is dead, the position is rigid.” You can see that Black’s bishop is on the same square color as the Black pawns (see Rule 2). We will discuss diagonals later, but as the White bishop controls the a5-e1 diagonal, this prevents Black from advancing the pawns and gives the White king the ability to block the Black king from invading the fortress. Also, the Black bishop cannot do anything to help on the dark squares. White’s fortress holds.

This is diagram No. 3 from page 232 of Lasker’s Manual of Chess³. Lasker gives “What a difference between this and the preceding position! The Black bishop and pawns complement each other, they work in harmony. Black wins with ease, say 1. Kd1 Bg4+ 2. Kc1 d3. White loses by zugzwang.” In this diagram the Black pawns are on the opposite color of the Bishop (Rule 2) and the bishop assists the advance of the pawns by controlling the b1-h7 and d1-h5 diagonals. The next elements of a BOC ending are the locations of the king and the bishop and how their role is defined in the fortress. We shall see that there are two basic types of fortress-the king’s and the bishop’s. To illustrate how these elements play out on the board we will look at two positions from Just the Facts! Winning Endgame Knowledge in One Volume¹.

This is Diagram No. 289 from page 229 of Just the Facts! Winning Endgame Knowledge in One Volume¹. Alburt gives” an impregnable king’s fortress — the defending king stops the passed pawn, while his bishop guards his own pawn on the other side of the board and prevents the creation of new passers.” Alburt also comments “No matter who is to move, Black holds easily.” We can see that Black follows Rule 1 with the same color for the pawn and bishop. Also note that the Black king is on a square that has an opposite color to the White bishop. It cannot be dislodged, and the game is drawn.

This is Diagram No. 293, attributed to Averbakh, from page 232 of Just the Facts! Winning Endgame Knowledge in One Volume¹. Alburt gives “a bishop’s fortress — the bishop stops the passed pawn while the king protects his own pawns and tries to prevent the creation of new ones. In a bishop’s fortress, the defender must stay especially alert.” Alburt continues “White can’t win because his opponent’s king and bishop block the king and pawns, for example,
1. Kc5 Ke6 2. Kb6 Kd7 3. b5 Kc8! Draw.”

Alburt summarizes the two fortresses with “In a king’s fortress, the defender’s king blocks the pawn. In a bishop’s fortress the bishop blocks the pawn. The king’s fortress is usually easier to hold.”

The reason for this is all in the elements. When the defender’s king is on a square of opposite color to the attacker’s bishop and in front of the passed pawn, the king cannot be dislodged or even approached by the attacker’s forces. In a bishop’s fortress, the attacker’s king can approach the defender’s bishop. The defender in a bishop’s fortress will have to be aware of any situation that results in the attacker’s king getting near the defender’s bishop. Otherwise, the fortress may collapse.

The last element we will consider in a BOC ending is a general rule for the defender’s bishop, sometimes known as the same diagonal principle.

This is Diagram No. 295, attributed to Averbakh, from page 233 of Just the Facts! Winning Endgame Knowledge in One Volume¹. Alburt gives “It’s always better when your bishop can do its work on one diagonal. In the above position, the bishop’s role is stopping White’s two passed pawns on the same diagonal (b8-h2) is particularly visible. Black’s bishop is ideally placed, and White can’t make any progress. 1. Kd5 Kf6 2. Kc5 Ke7 3. Kb5 Bf4 4. Kb6 Kd8, draw.” Alburt points out that moving the White pawn from f3 to g4 changes everything. Now Black’s bishop will not be able to hold both White pawns with one diagonal. The defense will fail.

That certainly was a lot of information about BOC fortress endings. For review, we have considered the following elements:

      1. the BOC's themselves

      2. the color relationship of the bishops with the pawns on the board

      3. determining the proper color and location of the square for the defending king

      4. the locations of the king and the bishop and how their role is defined in the fortress

      5. the same diagonal principle

Keep this list of elements in mind when looking at various positions or exercises.

It’s time to return to Ray Cheng’s position (Diagram No. 1) and look for the BOC elements in this position. Set up the original position and play the following moves: 1. ... f2 2. Bxf2 Bf3 3. h6 Kg6 and you should easily recognize these elements:

      1. The Black king blockades the White g5 and h6 pawns on a light-colored square.

      2. The Black bishop has the c6-h1 and c4-f1 diagonals available for defending the b5 pawn and supporting the king.

      3. The White bishop is the wrong color to attack the b5 pawn or the g6 king.

      4. The White king cannot attack the b5 pawn as the black bishop can run up and down on the c4-f1 diagonal.

      5. The White king cannot support the advance of the g5 and h6 pawns by itself.

I am sure you will find more details in this fascinating position.

Let’s take a look at a CCLA game with this type of ending.

1. e4 c6 2. c4 d5 3. exd5 cxd5 4. cxd5 Nf6 5. Nc3 Nxd5 6. Nf3 Nc6 7. Bb5 e6 8. O-O Be7 9. d4 O-O 10. Re1 Bf6 11. Ne4 Bd7 12. Bd3 Nce7 13. Ne5 Ng6 14. Nc5 Bc6 15. Nxg6 hxg6 16. Bf1 Nc7 17. Be3 Qd5 18. Qb3 Qxb3 19. Nxb3 Rfd8 20. f3 Nd5 21. Bf2 Rac8 22. Bc4 b6 23. Rac1 Bg5 24. Rcd1 Bf4 25. g3 Bd6 26. Nd2 b5 27. Bb3 Nb4 28. Ne4 Be7 29. Kg2 Bd5 30. Nc5 Bxc5 31. dxc5 Nxa2 32. Bxa2 Bxa2 33. b4 Rxd1 34. Rxd1 Bd5 35. Ra1 Rc7 36. g4 f6 37. Ra6 Rc8 38. Rxa7 Ra8 39. Rxa8+ Bxa8 40. Be3 Kf7 1/2-1/2

The players agreed to a draw here and for good reason, as we can already see the elements of a BOC fortress set-up on the queenside. The White dark squared bishop cannot attack the blockading Black pawn on b5, and the light-squared Black bishop will be able to defend the pawn from a diagonal. At the same time the Black bishop is holding the White protected passer on c5. If all of the pawns on the kingside are removed, the Black bishop can freeze the position along the c6-e8 diagonal, or the Black king can blockade the kingside at c6 without fear of an attack from the White bishop. All the players can do is move around in circles without making progress.

Stockfish evaluates this position as 0.00 = draw. Here is a projcted line: 41. h4 e5 42. Kf2 Ke6 43. f4 Kd5 44. fxe5 Kxe5 45. Bc1 Ke4 46. Kg3 Kd5 47. Kf4 Bc6 48. h5 gxh5 49. gxh5 Be8 50. Kg4 Bd7+ 51. Kf3 Kc4 52. Bd2 Be8 53. Kg4 Bd7+ 54. Kf4 Kd4 55. Be1 Kd5 56. Bh4 Ke6 57. Bg3 Kd5 58. Be1 Ke6 59. Bh4 Be8 60. Kg4 Bd7 61. Bg3 Kd5+ 62. Kf4 Ke6 63. Kf3 Be8 64. Kg4 Kd5 65. Bd6 Ke6 66. Bf4 Kd5 67. Bd2 Kc4 68. Kf5 1/2-1/2

References

1. Alburt, Lev, Krogius, Nikolay, Just the Facts! Winning Endgame Knowledge in One Volume , W.W. Norton, New York, 2001.

2. Cheng, Ray, Practical Chess Exercises, 600 Lessons from Tactics to Strategy, Wheatmark, Tucson, Arizona, 2007.

3. Lasker, Emanuel, Lasker’s Manual of Chess, David McKay Company, New York, 1947, (Dover Edition, 1960).

4. Mueller, Karsten, Lamprecht, Frank, Fundamental Chess Endings, Gambit Publications, London, 2001.