A windmill is a tactic where a piece swings back and forth giving discovered check each way, forcing the king to dodge while a rook gobbles material every cycle.
The engine of a windmill is a battery: a rook lined up behind a bishop. When the bishop steps aside the rook gives check; the king must move, the bishop returns with check, and the rook is free to grab another piece before it all repeats.
Because every move in the cycle is check, the opponent can never pause to defend — they just shuffle the king out of check while you strip the board of pieces one capture at a time.
The most famous example is Carlos Torre against Emanuel Lasker in 1925, where a windmill harvested several pawns and a queen. Spotting the rook-and-bishop battery is the key to setting one up.
A repeating series of discovered checks — usually a rook behind a bishop — that forces the king to keep moving while the rook captures more material on each turn.
Torre versus Lasker, Moscow 1925, where a rook-and-bishop windmill swept up several pawns and Black’s queen.
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