What is the Vancura position?
It is a rook ending with one pawn on the edge of the board. The a-file and the h-file pawns are called rook's pawns.
The attacking side has a king, a rook and the pawn on the sixth rank. The rook stands in front of its own pawn, which means it is stuck there.
The defending side has a king and a rook, and draws by putting the rook on the sixth rank beside the pawn.
Why does the rook attack from the side?
A rook on the sixth rank does two jobs from one square.
- It attacks the pawn along the rank, so the white rook has to stay in front of the pawn to guard it.
- It is far from the enemy king, so it can give checks from the side without being chased.
A rook behind the pawn on a1 does neither. It cannot check the enemy king on the queenside, and it never attacks the pawn from a useful square.
Where should the defending king stand?
Near g7. The king stays on the far side of the board, away from the pawn.
That sounds wrong, but there are two good reasons. The king is safe from checks over there, so Black is never forced to break the set-up.
It also keeps the king off the squares the rook needs. The rook has to be free to run up and down the f-file and along the sixth rank.
How the checks work
Follow the study one move at a time.
1. 1.Kd5 Rf5+ The white king steps forward and gets a check.
2. 2.Kc6 Rf6+ Black returns to the sixth rank with check. Once the king leaves that rank, the rook attacks the pawn on a6 again.
3. 3.Kb7 Rf7+ Another side check, and the king still has no quiet move.
4. 4.Kb8 Rf6 Back to the sixth rank. White has made no progress at all.
The white king cannot come close enough to drive the rook away, because every step is answered by a check from a safe distance.
What if the rook goes behind the pawn instead?
Then Black loses, and the second chapter of the study shows how.
A rook behind the pawn on a1 has no checks from the side. The enemy king is on the queenside, and the rook is on that side too.
The white king simply walks to b7. Once it stands on b7, next to its own pawn, the white rook is free. The pawn then goes to a7 and to a8.
The mistake we see most often
Learners put the rook behind the enemy pawn out of habit, because behind the pawn is the right place almost every other time.
Against a rook's pawn on the sixth rank with the enemy rook in front of it, the side attack is better. That is the whole reason this position has a name.
Check two things before you choose. Is the pawn an a-pawn or an h-pawn, and is it already on the sixth rank? If both are true, go to the side.