In honor of today's Olympic marathon, here's a look back at the origin of the race, plus an explanation of the whole ".2" business.

Olympic Marathon, 1908 London Games/

In 490 BC, a soldier named Pheidippides supposedly ran from the battlefield at Marathon to the city of Athens to alert the troops of a Greek victory. He then died of exhaustion, becoming the first of the estimated eight-per-1,000,000 marathon-related casualties.

While some scholars argue that the story of Pheidippides is merely historical myth, he does appear in a number of incidents in recorded history. Herodotus mentions a professional running courier named Pheidippides in his account of the Battle of Marathon, but says he ran from Athens to Sparta. Other historical accounts by Plutarch and Lucian in the 1st and 2nd centuries, respectively, tell the story of a runner by a different name who ran from Marathon to Athens.

Olympic Marathon, 1908 London Games/Getty Images

Our modern understanding of the figure comes from the 1878 poem “Pheidippides” by Robert Browning, which was most likely a composite of the runner mentioned by Herodotus and that of the two latter historians.

The modern marathon is entirely a creation of the organizers of the inaugural Athens Olympics in 1896, who used Pheidippides' legend as inspiration for a headline-grabbing gimmick. Runners followed a 24.85-mile (40-km) route beginning in Marathon and ending at the site of a stadium used in ancient times. This course was repeated in the 2004 Athens Olympics, and again in 2010 when 10,000 runners commemorated the 2,500th anniversary of Pheidippides’ trek. Cartographers and historians now theorize that his run was actually closer to 20 miles.

Why Is the Modern Marathon 26.2 Miles?

The 1908 Summer Games were initially awarded to Rome. There was concern that Italy wouldn’t be able to host the Olympics due to economic problems, but when Mt. Vesuvius erupted in 1906 and the country needed to rebuild the ravaged area, the Italian government requested that the Games be relocated. London took on the challenge of setting up shop on short notice, and subsequently changed the marathon forever.

The British Royal Family wanted the race to begin beneath the windows of the nursery at Windsor Castle and finish opposite the royal viewing box at the Olympic stadium. A few hundred yards were tacked on to accommodate the request, and the marathon would later be standardized at that distance—26 miles and 385 yards.

More Photos From the 1908 London Olympic Marathon

Doctors examine athletes before the race.

Runners enter Windsor Castle for the start of the 1908 Olympic Marathon. Getty Images

And they're off! Getty Images

Spectators climb trees in Wormwood Scrubs for a better view. Getty Images

Dorando Pietri of Italy is leading as he approaches the end of the race. Getty Images

Dorando Pietri, on the verge of collapse, is helped across the finish line. He was subsequently disqualified. Getty Images

U.S. athlete Johnny Hayes finished second, but was declared the winner. Getty Images

Hayes is carried by teammates after his victory. Getty Images

Pietri of Italy is taken away in a stretcher. Getty Images

Queen Alexandra presents Pietri a special Gold Cup after he was disqualified. Getty Images

Pietri and his Gold Cup. Getty Images

Johnny Hayes (left) and Dorando Pietri. Getty Images