Lesson
White to move. Main line: 1. Rh8#
The rook checks from h8 and the king cannot step aside: moving to f8 does not escape the rook, because once g8 is vacated the rook sees straight down the rank.
The pawn on g7 blocks the square directly in front of the king, and the white king on g6 covers f7 and h7. Three attackers, each doing exactly one job, and none of them redundant.
It is worth comparing with the ordinary back-rank mate: there the defender’s own pawns build the cage, here the attacker brings it. The geometry is the same — the difference is who supplied the walls.
A back-rank mate the attacker builds
The ordinary back-rank mate works because the defender boxed itself in with its own pawns. Anderssen’s mate is the same geometry with the walls supplied by the attacker: a pawn on g7 blocks the square in front of the king, and the attacking king covers the two squares beside it.
It is named after Adolf Anderssen, the nineteenth-century attacking player whose casual game against Kieseritzky is still called the Immortal Game.
The move that looks like an escape
The instructive detail is f8. At a glance it looks free — the rook on h8 seems to be blocked by the king standing on g8. It is not: the moment the king steps aside, the rook sees straight down the rank, so the flight square was never real.
This is worth internalising in both directions. As the attacker it means a rook check along a rank is stronger than it looks; as the defender it means a square shielded by your own king is not a flight square at all.
Three attackers, no spare parts
The rook checks, the pawn blocks, the king covers f7 and h7. Remove any one of the three and the mate disappears — which makes this a good position for practising how to assess a mating net rather than just recognising one.
Ask of each attacking piece what would happen without it. If the answer for some piece is "nothing", the net is looser than it looks and the defender probably has a resource.
A square shielded by your own king is not an escape square — the attacker sees through it once the king moves.
Mating nets are built from attackers with distinct jobs. Check each one earns its place.
The attacking king is a mating piece in the endgame. Bringing it up is not risky there, it is the plan.
Source: Checkmate patterns — https://en.wikipedia.org/wiki/Checkmate_pattern
Source: Adolf Anderssen — https://en.wikipedia.org/wiki/Adolf_Anderssen