It was actually originally 24.8 miles in the 1896 olympics , which was the real distance between marathon and athens before the soldier collapsed and died..
The marathon distance changed as a result of the 1908 Olympic Games in London, England. That year, King Edward VII and Queen Alexandria requested that the marathon begin at Windsor Castle (20 miles west of central London), so that the Royal family could view the start. The course distance between the castle and the Olympic Stadium in London was 26 miles. Event organizers added an extra 385 yards around the stadium track, so the competitors would finish directly in front of the King and Queen's royal viewing box. Every Olympic marathon run since the 1908 Games has been a distance of 26 miles, 385 yards,
Night Nurse - thanks for that - I had always thought it had been 26 miles before 1908 and the 385 yards, which was added for the Royal family as you say, was originally intended as a one off. Of course what subsequently happened meant that the 385 yards was added forever.
Dorando Pietri entered the stadium in the lead but went the wrong way and then collapsed a few times so was helped over the line by some officials - Jonny Hayes finished second but complained about the assistance that Pietri had received and he was disqualified so the 385 yards became crucial to the result.
I think after the Olympics they both ran against each other for money over the 26 miles and 385 yards and the current Marathon distance was born. Of course this race also led to a massive explosion in Marathon running which still exists today.
Although I haven't been tempted yet!!