After the Downfall by Harry Turtledove

Harry Turtledove posits a typical Nazi soldier, in the last days of the defense of Berlin in 1945...Hasso Pemsel...who is supposed to defend to the death the ruins of the old Berlin Museum. All of the antiquities have supposedly been taken to safety in bunkers, but he finds a big rock that he hides behind, taking refuge from the Russian sharpshooters. He sees the information sign is still there, and it says that the big rock is the Omphalos stone, from the temple of Apollo at Delphi. He crawls on top of it and disappears.