The word "marathon" began as a place name. Marathōn was a coastal plain in Attica, about 26 miles north-east of Athens, named after the wild fennel (marathon) that grew there. In the late summer of 490 BCE, a small Athenian army defeated a much larger Persian invading force on that plain — and the place name was destined for a curious afterlife.
The Run That Probably Did Not Happen
According to a story popularised centuries later, an Athenian messenger named Pheidippides ran from the battlefield at Marathon to Athens to announce the victory, gasped out the word nenīkēkamen ("we have won"), and dropped dead. It is a wonderful story. It is also, almost certainly, a literary embellishment of an earlier and more plausible account by Herodotus, in which Pheidippides ran from Athens to Sparta — a much longer 150-mile journey — before the battle, to ask for reinforcements.
Reviving the Race in 1896
When the modern Olympic Games were planned for Athens in 1896, the organisers wanted a long-distance running event with classical resonance. The French scholar Michel Bréal proposed a race based on the legend, running from the actual plain of Marathon to the Athens stadium. The first marathon was run in April 1896 over roughly 25 miles, and was won by a Greek water-carrier named Spyridon Louis. The exact distance of 26 miles 385 yards (42.195 km) was fixed only in 1908, at the London Olympics, to bring the finish line in front of the royal box at White City Stadium.
A Word for Endurance
By the 1920s, "marathon" was no longer just a foot race. English speakers used it figuratively for any test of endurance: a marathon meeting, a marathon negotiation, a marathon bake. The Greek place name has shed almost all its geographic meaning to become a metaphor for length and grit.
The Suffix "-athon"
So firmly was "marathon" identified with endurance that English speakers extracted a brand-new suffix from it. In the 1930s came walkathon and danceathon, modelled on the marathon's "long, gruelling event" sense. By the 1950s and 1960s it was generating read-a-thon, telethon, and hackathon. None of these have anything to do with Greek — they are all the children of the legend of Pheidippides.