What equestrian competition is referred to as the equine sport version of the triathlon?

Three Day Eventing or commonly called Eventing or Horse Trials, is a popular worldwide equestrian competition that tests three different phases of disciplines during the event: dressage; cross country or XC; and stadium jumping. Originally, eventing began during the military era when horses were needed for military operations. The above disciplines were used to test the skills, fitness and suitability of both horse and rider. Dressage was a necessary discipline used to train the horse and rider for parade skills and formations needed on the battle field. Cross country and stadium jumping was used to test the horse and rider for stamina, speed and endurance over obstacles such as fences, creeks and hills that may be encountered during a military operation.

In 1912, eventing became an Olympic sport at the Stockholm games. Only uniformed male commissioned officers were allowed to compete until the 1950's. By 1964, the first women competed on the US team at the Tokyo games.

Much has evolved in eventing since then. Roads and Tracks and the Steeplechase phases have been eliminated. Safety concerns for both rider and horse have taken a forefront with vet checks prior to each discipline; changes in the design of XC fences to prevent rotational falls; and penalties for excess speed on the course have been added.