Mate With Two Rooks

You know what checkmate is; now let's build one from scratch. Two rooks against a lone king is the simplest forced mate in chess, and players call it the ladder (or the lawnmower): the rooks climb the board like two rails, one rank at a time.

The rook on b4 is the fence: the king cannot cross rank 4. Now Ra5, rook to a5, checks and forces him back a rank.

The two rooks share two jobs. One is the fence, holding a rank the king may not cross. The other gives the check, one rank beyond the fence, so the king's only choice is to retreat. After the check, the checking rook becomes the new fence, and its partner is free to check again:

One rank later, roles swapped. The a-rook holds rank 5, so Rb6 checks and pushes the king to rank 7.

Rank by rank the ladder climbs. Keep both rooks far away from the king, over on the a- and b-files here. If the king ever marches toward one to attack it, slide that rook all the way across to the other side of the board, same rank, and carry on. He can never catch both.

The top of the ladder. Ra8 is checkmate: one rook owns rank 8, the other seals rank 7, and the edge of the board does the rest.