Marathon from the start at Windsor Castle to the royal entrance to the White City Stadium, followed by a lap (586 yards 2 feet; 536 m) of the track, finishing in front of the Royal Box. The course was later altered to use a different entrance to the stadium, followed by a partial lap of 385 yards to the same finish. The modern standard distance for the marathon was set by the International Amateur Athletic Federation (IAAF) in May 1921 directly from the length used at the 1908 Summer Olympics in London. An official IAAF marathon course is 42.195 km (42
Athletics at the 1908 Summer Olympics – Men's marathon at the Olympic Stadium, the Great White City Stadium in Shepherd's Bush in London. The Polytechnic Harriers were also tasked with organising a Marathon Trial Race, to be run along most of the Olympic Marathon route. By April 1908, a revised map of the course of the Trial Race was published, also showing the intended course of the Olympic Marathon. It had by this time been decided to fix the Olympic Marathon distance at "about 26 miles" to the stadium, plus a lap of the track (), using the Royal Entrance as the marathon tunnel, and finishing at the normal