Lesson
White to move. Main line: 1. e4 e5 2. f4 exf4 3. Bc4 Qh4+ 4. Kf1 b5 5. Bxb5 Nf6 6. Nf3 Qh6 7. d3 Nh5 8. Nh4 Qg5 9. Nf5 c6 10. g4 Nf6 11. Rg1 cxb5 12. h4 Qg6 13. h5 Qg5 14. Qf3 Ng8 15. Bxf4 Qf6 16. Nc3 Bc5 17. Nd5 Qxb2 18. Bd6 Bxg1 19. e5 Qxa1+ 20. Ke2 Na6 21. Nxg7+ Kd8 22. Qf6+ Nxf6 23. Be7#
The sacrifices are not isolated tricks. Anderssen keeps adding developed pieces to the attack while Black spends time collecting material with the queen. By move 18, White’s rook and queen can disappear because the black king has no defenders ready.
The final queen offer, 22.Qf6+!, forces 22...Nxf6 and clears e7. Then 23.Be7# completes a mate delivered by two bishops and a knight while White has neither queen nor rook.
The game is a vivid lesson in attacking priorities: material only matters when there is time to use it. King safety, development and forcing moves can outweigh an apparently enormous deficit.
A throwaway game that outlived its tournament
Anderssen and Kieseritzky played this in London in 1851 as a casual game, in a break during the tournament — not as a competitive encounter. It is a fair guess that neither expected it to be remembered.
It became the most reproduced game in chess literature anyway, because it shows an idea in its purest form: material is worth exactly what it can do, and pieces that are doing nothing are worth nothing at all.
The arithmetic of the sacrifice
By the end White has given away both rooks, a bishop and the queen. Count what is left: three minor pieces, all of them touching the black king. Black meanwhile owns a queen, two rooks and a bishop, and almost none of them can reach the kingside in time.
That is the whole argument. Anderssen is not being reckless with material; he is trading pieces that would need four moves to matter for pieces that matter immediately.
What modern analysis changed
Engines have since found improvements for Black — the defence was not perfect, and parts of the attack are not forced. This is normal for nineteenth-century brilliancies and does not diminish the game.
What survives analysis is the judgement, not the calculation. Recognizing that an attack is worth more than the material it costs is a decision a player makes; verifying it move by move is what the engine is for.
Material only counts when it can participate. A rook on a1 defending nothing is not a rook.
Sacrifices are a trade of material for time. Ask what the extra tempo buys before you ask what the piece cost.
A famous attacking game is a model of judgement, not a line to memorize.
Source: The Immortal Game — https://en.wikipedia.org/wiki/Immortal_Game
Source: Adolf Anderssen — https://en.wikipedia.org/wiki/Adolf_Anderssen
Source: Lionel Kieseritzky — https://en.wikipedia.org/wiki/Lionel_Kieseritzky