What is the longest checkmate known to mankind?

Regards,
Janos

@TheKingClash said in #2:
> 1. Nf3 Nf6 2. Ng1 Ng8 3. Nf3 Nf6 4. Ng`1 Ng8 5. Nf3 Nf6 6. Ng1 Ng8 7. Nf3 Nf6 8. Ng1 Ng8... repeat until ............ 314496. Ng1 Ng8 314497. e4 Nh6 314498. Bc4 Nc6 314499. Qh5 Ng4 314500. Qxf7#
1. Either threefold repetition or the 50-move rule would cause a tie.
2. EVEN if you don't consider #1 , you could still technically checkmate on the 314502th move.

Assuming both players avoid 3 fold repetition:

50th move: move a white pawn #move the white pawns to row 2
100th move: move a white pawn
...
450th move: move a white pawn #move the white pawns to row 3
500th move: move a white pawn
...
1600th move: move a white pawn #now all the white pawns are pushed up against the black pawns
1650th move: capture a black pawn #with a knight so that you don't have to move pawns
...
2000th move: capture a black pawn #now all the black pawns are gone
2050th move: capture a black piece #start cannibalizing on black's pieces
...
2350th move: capture a black piece # now all the black pieces are in pieces.
2400th move: move one of white's edge pawns #the 'a' or 'h' pawn
2450th move: promote that pawn # to a knight so there won't be any accidental checkmates
2500th move: move the pawn next the promoted one #the 'b' or 'g' pawn
2550th move: promote that pawn # to a knight again and now the black king can escape
2600th move: move a white pawn #to the 7th row now
...
2850th move: move a white pawn # now all the white pawns are on the 7th row
2900th move: promote a pawn #again to a knight so that we don't accidentally checkmate early
...
3150th move: promote a pawn # now all of whites pawns are promoted
3200th move: capture a white piece #there are 14 to capture because we need to leave the queen for the checkmate
...
3900th move: capture a white piece #now only the kings and the white queen remain
3950th move: checkmate #fun fact: if you add up the value for all the pieces for one side you get 39

Let me know if I made a mistake anywhere :)

Fivefold repetition is an automatic draw, even if not claimed. Same with 75 moves under 50-move-rule conditions.

As such, the longest possible game would have 6*8 pawn moves for each side, and 15 captures for each side, for a total of 12*8+30 = 126 resets of the 50-move counter -- except 8 of the pawn moves have to be captures (of non-pawns or already-promoted pawns) to free the opposing pawns, so that's 118, times 75 is an upper bound of move 8850. That's not the max, though, because these can't all be resets done by the same player. The best I can see happening is somewhere around white's 8849th move.

It's an open question as to whether the starting position is a forced checkmate, though the popular consensus is that it's a forced draw. Some googling yields tb7.chessok.com/probe/3/61 as the longest forced checkmate at 549 moves.

Thank you for the answers! Very interesting! Also @LeoHao's answer Is very interesting!