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
Bangkok Marathon course passes many historical landmarks of cultural and ethnic importance. The marathon starts and finishes in front of The Royal Grand Palace at Sanam Chai Road. The race course is sanctioned by The Association of International Marathons and Distance Races (AIMS) and the Amateur Athletic Association of Thailand (IAAF Rules). In 2013, the course of the half marathon was changed at the last minute because of concurrent Bangkok street protests which reduced the distance of the half marathon from 21.1 km (13.1 miles) to 19.7 km (12.2 miles). In 2015, the half marathon was accidentally extended from 21.1 km (13.1