Marathon appeared in the late 19th century. Till then the race distance was inconsistent for the game. During the first Olympic Games in 1896, runners jogged along Pheidippides’s old route for a distance of 40,000 meters which is equal to 24.85 miles. (That race, by the way, was won by a Greek postal worker.) The next Olympic Games saw the distance bumped to a pinch over 25 miles. And while subsequent marathons hanged around the 25-mile mark, no standard distance was ever codified.
Then the Olympics came to London. In 1908, the marathon, which stretched between Windsor Castle and White City Stadium in London, lasted 26.2 miles—all for the benefit of England's royal family so that they can enjoy the game in an ease.
Like previous races, the original event was supposed to cover a ballpark of 25 miles. The royal family, however, had other plans: They wanted the event to start directly in front of their—as the story goes, the royal children wanted to see the start of the race from the castle nursery. Officials of the game duly agreed and moved the starting line, tacking on an extra mile to the race.
As for the pesky final 0.2? That was the British royal family’s fault, too. The finish line was extended an extra 385 yards so the race would end in front of the royal family’s viewing box.
But those extra 1.2 miles proved to be a curse. The race’s leader, an Italian pastry chef named Dorando Pietri, collapsed multiple times during the run towards the finish line and had to be helped to his feet. One of the people who came to his aid was Arthur Conan Doyle, a journalist. Afterward, Conan Doyle wrote about Pietri's late-race struggles for the Daily Mail, saying, “Through the doorway crawled a little, exhausted man ... He trotted for a few exhausted yards like a man galvanized into life; then the trot expired into a slow crawl, so slow that the officials could scarcely walk slow enough to keep beside him.”
After that Olympics, the distance of most marathons continued to hover between 24 and 26 miles, but it seems that Conan Doyle’s writing may have brought special attention to the distance of 26.2, endowing it with a legendary “breaker-of-men” reputation. Indeed, when the International Amateur Athletic Federation convened to standardize the marathon, they chose the old London distance of 26 miles and 385 yards—or 26.219 miles.