Prior to 1908, marathon distances in the modern Olympic Games were largely approximate, usually measuring around 25 miles depending on the local geography of the host city. When London hosted the IV Olympiad in 1908, the Polytechnic Harriers were tasked with mapping out a grand course that would highlight British landmarks. Originally, the organizers planned a 26-mile race beginning on the lawns of Windsor Castle and finishing in front of the Royal Box inside the newly built White City Stadium.
However, British Royal preferences intervened to alter sporting history. Princess Mary requested that the starting line be moved so that the young Prince Edward and Prince Albert could view the commencement of the race directly from the window of the Royal Nursery on the East Lawn of Windsor Castle. This minor shift added roughly 385 yards to the beginning of the route.
To ensure the race concluded dramatically right in front of King Edward VII's royal viewing stand inside the stadium, the overall distance was finalized at exactly 26 miles and 385 yards (42. 195 kilometers). The 1908 race became legendary due to the dramatic collapse of Italian runner Dorando Pietri near the finish line, fixing the 26.
2-mile distance in the public imagination. In 1921, the International Amateur Athletic Federation officially adopted the 1908 London length as the world standard for all future marathons.