The marathon was one of the original modern Olympic events in 1896, though the distance did not become standardized until 1921. More than 800 marathons are held throughout the world each year, with the vast majority of competitors being recreational athletes as larger marathons can have tens of thousands of participants.
The name Marathon comes from the legend of Philippides or Pheidippides, the Greek messenger. The legend states that he was sent from the battlefield of Marathon to Athens to announce that the Persians had been defeated in the Battle of Marathon (in which he had just fought), which took place in August or September, 490 BC. It is said that he ran the entire distance without stopping and burst into the assembly, exclaiming νενικήκαμεν (nenikēkamen, "we have won!"), before collapsing and dying. The account of the run from Marathon to Athens first appears in Plutarch's On the Glory of Athens in the 1st century AD, which quotes from Heraclides Ponticus's lost work, giving the runner's name as either Thersipus of Erchius or Eucles. Lucian of Samosata (2nd century AD) also gives the story, but names the runner Philippides (not Pheidippides).
There is debate about the historical accuracy of this legend. The Greek historian Herodotus, the main source for the Greco-Persian Wars, mentions Philippides as the messenger who ran from Athens to Sparta asking for help, and then ran back, a distance of over 240 kilometres (150 mi) each way. In some Herodotus manuscripts, the name of the runner between Athens and Sparta is given as Philippides. Herodotus makes no mention of a messenger sent from Marathon to Athens, and relates that the main part of the Athenian army, having fought and won the grueling battle, and fearing a naval raid by the Persian fleet against an undefended Athens, marched quickly back from the battle to Athens, arriving the same day.
In 1879, Robert Browning wrote the poem Pheidippides. Browning's poem, his composite story, became part of late 19th century popular culture and was accepted as a historic legend.
Mount Pentelicus stands between Marathon and Athens, which means that if Philippides actually made his famous run after the battle, he had to run around the mountain, either to the north or to the south. The latter and more obvious route matches almost exactly the modern Marathon-Athens highway, which follows the lay of the land southwards from Marathon Bay and along the coast, then takes a gentle but protracted climb westwards towards the eastern approach to Athens, between the foothills of Mounts Hymettus and Penteli, and then gently downhill to Athens proper. This route, as it existed when the Olympics were revived in 1896, was approximately 40 kilometres (25 mi) long, and this was the approximate distance originally used for marathon races. However, there have been suggestions that Philippides might have followed another route: a westward climb along the eastern and northern slopes of Mount Penteli to the pass of Dionysos, and then a straight southward downhill path to Athens. This route is considerably shorter, some 35 kilometres (22 mi), but includes a very steep initial climb of more than 5 kilometres (3.1 mi).