The longest chess game ever played was between Ivan Nikolić and Goran Arsović. The game was 269 moves long. It lasted for 20 hours and 15 minutes and ended in a stalemate.
I actually witnessed a game that was longer! Seriously. It was 20 hours and 55 minutes. It was 224 moves. I assume it's the number of moves that counts for the world record?
I have been not around for a long time if you have then please tell me