Why is a marathon 42.2 kilometers?

In the world of endurance running, the marathon is sort of the gold standard. Many other races are titled based on their length relative to this classic event. We have short, half, and ultra varieties in addition to the standard 42.2 kilometer race we've all come to know and love. But, if you stop and think about it, that's a pretty strange number. Why is a marathon 42.2 kilometers long?

Thank Pheidippides

Wait, who?

Although the exact details of the story — and precisely who first recorded it — is a matter of debate among historians, the length of the modern marathon can be traced back to an Athenian runner named Pheidippides. Said to have lived between 530 and 490 B.C., Pheidippides had the very impressive job of being a hemerodrome, or "day-long runner," for the Athenian army during the Persian Wars.

According to the original stories, Pheidippides was really, really good at what he did. One account has him covering some 250 kilometers through the Greek countryside in just 36 hours. Which is amazing. The portion of his story that has a direct bearing on our modern marathon, however, is the last leg of his exploits: the trip he made from a small town named ... wait for it ... Marathon to Athens in order to announce the Greek victory over the invading Persian army.

But, that's only 40 kilometers. How'd we get the additional 2.2 tacked on to the already challenging race? Bear with me, we'll get there — marathons are all about pacing, after all.

The first Olympic marathon

While the story of Pheidippides had its place in Greek history and myth, the ancient Greeks didn't have an official marathon the way we know it now. That started at the 1896 Olympic games, hosted in Athens. At that original event, a French linguist named Michel Breal suggested an endurance event to commemorate the story of Pheidippides by literally running from Marathon to Athens, old-school style. This course was 39.9 kilometers long, though.