A marathon is a long distance running event which has a distance of 42.195 KM. (or 26 miles 385 yards). This is also an Olympic event. While the Marathon was one of the events at the 1896 Olympics, the distance did not get standardised until the 1921 marathon. The event itself derives its origin from the Battle of Marathon and the story of Pheidippides who was a messenger.
Today the event has grown to all the part of the world with multiple running events across the globe. The current marathon world record is held by Dennis Kimetto of Kenya who won the Berlin marathon in 2014 in a time of 2 hours 2 minutes and 57 seconds. There are six world marathon major races in the world, which are basically the marathons at the following cities ? Tokyo, Boston, London, Berlin, Chicago and New York. (http://www.worldmarathonmajors.com/)
With thousands of people running the marathon these days, there is more and more stress on detailed marathon training. Marathons are also getting popular in India with the number of events increasing manifold.