marathon (n.) Look up marathon at Dictionary.com
1896, marathon race, from story of Greek hero Pheidippides, who in 490 B.C.E. ran the 26 miles and 385 yards to Athens from the Plains of Marathon to tell of the allied Greek victory there over Persian army. The original story (Herodotus) is that he ran from Athens to Sparta to seek aid, which arrived too late to participate in the battle. Introduced as an athletic event in the 1896 revival of the Olympic Games, based on a later, less likely story, and quickly extended to mean "any very long event or activity." Related: Marathoner (by 1912).