The first modern Olympic marathon was 42.195 km long.

False. At the first modern Olympic Games in Athens in 1896, the marathon race was approximately 40 kilometers long, which was the historic route from Marathon to Athens. The exact distance of 42.195 kilometers was only standardized in 1921 by the International Amateur Athletic Federation (IAAF), after that distance had been used at the 1908 London Olympics. There, it was slightly extended from the planned route to finish in front of the royal box at White City Stadium.