The marathon race is 26 miles (42km) long, because that was the distance run by a messenger from the Battle of Marathon to Athens in 490 BC.

The “truth”

Pheidippides (or Philippides) was, according to contemporary accounts, a professional long-distance runner sent from Athens to Sparta to ask for help in the forthcoming battle against the Persians. (The Spartans refused, incidentally, because they were having a holiday, but the messenger met the god Pan on the way back, so his journey wasn’t entirely wasted). Pheidippides’s two-day journey was of around 150 miles (240km). A legend first recorded centuries later had him also running 24 (or 25) miles (39–40km) from the battlefield to Athens, to bring news of the victory (and heroically drop dead having done so.) This was, approximately, the course taken by the first ever marathon race, at the 1896 Olympic Games in Athens.

At the 1908 Games in London, the race was run from Windsor Castle to White City Stadium, a distance of 26 miles, with an extra 385 yards (352m) added to ensure that the finishing line was in front of the royal box. This London length of 26 + 385 was finally adopted as the international standard for all marathons, Olympic and otherwise, in 1921.

Whatever did or didn’t happen in ancient Greece, the 26-mile race was definitely invented in London, not Athens.