Lucena position: how to build a bridge and win

In the classic Lucena position, four conditions come together:

• The attacking pawn is on the seventh rank and is not a rook pawn.
• The attacking king stands on the promotion square, in front of its own pawn.
• The defending king is cut off from the pawn by at least one file, here by the white rook on the e-file.
• The defending rook stops the white king from leaving on the other side, here from the c-file.

The problem for White is simple to state. The king has to leave d8 so the pawn can promote, but as soon as it steps out, the black rook gives check from behind. Without shelter, the king can never escape the checks. The solution is to prepare a shelter in advance with your own rook.

White first drives the black king one more file away, then places the rook on the fourth rank. The king walks out towards the rook, and when the black rook runs out of useful checks, the white rook steps in between and blocks the last check. That rook is the bridge: it shields the king from the checks along the file.

Why the fourth rank? The white king needs the fifth rank to step out of the checks, and the rook on the fourth rank then blocks one square below it. If you remember one rule, remember this one: with the pawn on the seventh rank, the bridge goes on the fourth rank. On the tablebase page this position appears as an example; here you learn the full method.

• Black brings the king closer. After 2.Rf4, Black can play 2...Kg6 instead of waiting. The plan does not change: 3.Ke7 Re2+ 4.Kd6 Rd2+ 5.Ke6 Re2+ 6.Kd5 Rd2+ 7.Rd4. The tablebase confirms the win after every move of this line.
• Black attacks from the side. After 3.Ke7, the move 3...Rc7 pins the pawn along the seventh rank. White answers 4.Kd6, attacking the rook. Black has to take with 4...Rxd7+ 5.Kxd7, and king and rook against king is a basic mate.
• The king walks out too early. After 1.Rf1+ Kg7, the move 2.Ke7 is still a win according to the tablebase, but it achieves nothing: after 2...Re2+ the king either goes back to d8 or faces a long series of checks. The tablebase also counts more moves to the win than after 2.Rf4.
• Other rook squares. In the position after 1...Kg7, the tablebase also shows 2.Rf5 and 2.Rf3 as winning. The fourth rank is the method that works in the standard Lucena set-up, so practise that one first.

In the starting position, several white rook moves keep the win. 1.Rf1+ is the move that starts the clearest plan.

The bridge needs all four conditions. If one is missing, the result can change completely.

• The defending king is in front of the pawn. Then the position is not a Lucena position but a drawing set-up for the defender. The method for that is the Philidor position.
• The pawn is a rook pawn. With the king on a8 and the pawn on a7, the king can only leave via b8 or b7, and the black king can stay close to those squares.

With the black rook on the b-file, the tablebase shows a draw in this set-up when the black king is on c7, d7 or e7. Only when the black king is cut off further, on f7 in our test, does White win. With a rook pawn, the defending king does not have to be close; it only has to be close enough.

1. Open the first diagram with "Play this position against Stockfish" and win it as White against the Grandmaster level on the play against Stockfish page.
2. Play it again and let Black defend differently each time: check early, bring the king closer, wait with the rook.
3. Set up the same structure on another file in the board editor. With a knight pawn, for example king b8, pawn b7, rook c1 against king d7 and rook a2, the bridge works the same way: 1.Rd1+ Ke7 2.Rd4, and the rook later blocks on b4. The tablebase confirms the win after every move of that line.
4. Then switch sides: set up a position where you defend with Black and see how quickly Stockfish builds the bridge.
5. Finally, compare with the rook pawn diagram above and with the Philidor position, so you know which rook endgames are wins and which are draws.