Races over short distances, or sprints, are among the oldest running competitions. The first 13 editions of the Ancient Olympic Games featured only one event, the stadion race, which was a race from one end of the stadium to the other. Sprinting events are focused on athletes reaching and sustaining their quickest possible running speed. Three sprinting events are currently held at the Olympics and outdoor World Championships: the 100 metres, 200 metres, and 400 metres. These events have their roots in races of imperial measurements that later changed to metric: the 100 m evolved from the 100-yard dash, the 200 m distances came from the furlong (or 1/8 of a mile), and the 400 m was the successor to the 440 yard dash or quarter-mile race.