Eventing, sometimes described as an equestrian triathlon, became an Olympic summer sport at the Stockholm Games in 1912, but before that, it had its roots in the military as a series of exercises developed to test and prepare cavalry horses. Equestrian sports date back much further, in some cases all the way back to the ancient Olympics, which featured chariot and mounted races. Polo, too, has existed in some capacity for hundreds of years, and briefly became an Olympic event in the early 20th century, though it was removed from the program in 1936.

Eventing combines three phases — dressage, cross-country and show jumping — which must be completed within three days by the same horse and rider pair. Dressage is held first and is the most subjective of the three events: the rider takes the horse through a series of predetermined maneuvers in a ring, demonstrating discipline, rhythm, obedience, precision and grace to a panel of judges. The judges then each reward the rider...