"Twenty-five hundred years ago in 490 BC, a Greek herald named Pheidippides ran several dispatches totaling 240 km (150 miles) during the final two days of the Battle of Marathon. The distance of his final run from Marathon to Athens to deliver news of the Greek victory over the Persians with the word (we have won) is the basis for the marathon race being 42 km (26.2 miles). Insofar as Pheidippides ran those dispatches over mountainous terrain in hot weather and would have been 40 (born in 530 BC), it is not surprising that he collapsed and died moments later.
Nowadays, dying from running a marathon is rare, but developing rigor mortis, referred to as hitting the wall, is not.Typically this happens in the final fourth of the marathon when, because of glycogen depletion, muscle fibers lock up, effectively turning a runner into a staggering corpse."Source: