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In chess puzzles, the objective of the puzzle is usually to checkmate the opponent using some form of novel strategy or tactic. For example, the following puzzle (from here):

mate in two

has white to play and mate in two.

But this puzzle:

mate in sixty

is famous for having white to play and mate in sixty.

This puzzle got me thinking - what's the position with which either player can force mate that requires the most moves to do so?

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    $\begingroup$ Would be interesting to know not the starting position is the answer :) $\endgroup$ – Hagen von Eitzen Nov 8 '15 at 22:42
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    $\begingroup$ @HagenvonEitzen It's not known whether white has a winning strategy yet. $\endgroup$ – Joe Z. Nov 9 '15 at 0:28
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    $\begingroup$ @JoeZ. How do you mate in two in the first puzzle? Can't black sacrifice the rock to make us need a third move? $\endgroup$ – Nathan Jun 7 '17 at 14:33
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A bit of digging around finds a position at http://rybkaforum.net/cgi-bin/rybkaforum/topic_show.pl?tid=8477 taken from from one of the 7-piece endgame databases that's claimed as mate in 524 (though I found a few sources that contend that's only the 'time-to-win' and that actual mate could take substantially longer) :

enter image description here

However, this isn't a 'constructed' position; there's no theme to the mating sequence, and the moves are the classic 'no rhyme or reason' dance that shows up so much in these multi-piece endgames. As far as actual chess problems go, the longest I was able to find was a mate in 270, as seen at http://chess.eusa.ed.ac.uk/Chess/Trivia/Longestmate.html :

enter image description here

White starts with 1. Bb1: the core idea here is that White wants to gain access to a6; Black shuttles his king back and forth between a8, b7 and c8, as White plays Ka5-a4-a3-a2-a1, Ba2, Ka1-b1-c1-d1-e1-f1-f2-e1-d1-c1-b1-a1, Bb1, Ka1-a2-a3-a4-a5. Since White has 'lost a move' with the e1-f1-f2-e1 triangulation, Black now has to move a pawn in lieu of moving his King and giving White access to a6. Black's available pawn moves are Pf6-f5-f4, Pf7-f6-f5, Ph4-h3-h2, Ph7-h6-h5-h4-h3 before he finally runs out of pawn moves and must allow White access to a6 to queen his lead b-pawn.

(I should note that it's not clear to me that the opening move is unique and that White can't play Ka5-a4-a3 and then Bb1; I presume there's some rationale that prevents this cook, but I don't immediately see it.)

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  • $\begingroup$ In terms of that 524-step one, I'm assuming 1. Qxb7 is not the optimal move? $\endgroup$ – Joe Z. Jun 2 '14 at 21:52
  • $\begingroup$ @JoeZ. It is not, but I couldn't tell you why offhand. (That thread also contains a position with a longer sequence, which I should update this answer to at some point.) $\endgroup$ – Steven Stadnicki Jun 3 '14 at 6:53
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    $\begingroup$ @JoeZ The first diagram has a little black square in the top right corner. This indicates that it's Black's move. Even though chess problem genres have conventions as to who moves first, people reporting positions in chess tablebases may give a WTM or a BTM position. $\endgroup$ – Rosie F Aug 6 '16 at 19:47
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    $\begingroup$ Petrovic's #270 above is in Fox & James's The Complete Chess Addict, which gives some of the moves. As Steve says, Black, when out of pawn-moves, must allow White Ka6. White threatens Ka6 only when wK is on a5. The point of 1 Bb1 is that wK is on a5 now, so Black must push a pawn now. $\endgroup$ – Rosie F Aug 6 '16 at 20:17
  • $\begingroup$ if the fifty move rule is applied a player can claim a draw after at most ~300 moves. this applies to all seven piece endgames. $\endgroup$ – miracle173 Mar 14 '18 at 5:29

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