And from these origins we have the modern "eventing" (also known as "combined training) Like 'military' eventing tests the horse's suppleness and maneuverability, stamina and endurance and finally the horse's fitness and strength. These factors are tested through the 3 phases of an event; Dressage, Cross Country, Show Jumping (Stadium Jumping). For sure, eventing is probably one of the most 'specator appealing' equestrian sports.

The One Day Event: (ODE)
As explained by its name, the One Day Event occurs over one day. Usually this type of event is the more informal introduction to 3DEs (explained later) These are held mostly by pony clubs, or riding clubs of sorts. Anyhow, the ODE is comprised of the 3 phases: Dressage, Cross Country, and Show jumping. 

The 3-Day Event: (3DE)
Like the ODE, the 3DE is comprised of the 3 phases: Dressage, Cross Country, and Show jumping. BUT, the 3DE (like explained by its name) occurs of 3 days. Dressage is on the first day, followed by cross country on the second and show jumping on the third. 3DEs are most common in state/provincial or national/international level eventing competitions. 
 
 

Dressage is always held first (at the start of the day). The dressage phase consists of a ridden flatwork 'test' for horse and rider. Your aim is to get as high a percentage/score as possible; ride a precise/correct course . You will receive the test prior to the day of the event (the difficulty of the test will be allocated according to the level you wish to compete) You are expected to memorise the set of figures and movements in order. Each figure/movement will be marked out of 10, based on correctness, suppleness, position, obedience etc. The marks out of 10 will then be added up and given as your final score (or converted into a percentage). eg. If there are 10 sets of movements, it means that the perfect score will be 100. If you score 6 on each movement (it is highly unlikely you will score the same mark on each movement) that means you have achieved 60/100 or 60%. You will get penalties for errors of course or test.

Cross Country is the next phase. This consists of a course over different terrain with built/solid jumps (or naturally fallen logs etc.). You will receive a map of the course and will be able to walk the course either the day before the event or in the morning before the first horse has begun the phase.  Your aim is to ride the course without gaining any penalties or time faults ie.as quickly and correctly as possible.

Show Jumping is the last phase of the event. It tests the horse's and rider's ability to still 'function' after the strain of the last 2 phases. This held in an 'enclosed' area or arena where jumps are set up (the height according to the level in which you are competing) in a particular course; the jumps being composed of poles and wings.  Your first aim is to complete the course without getting any faults. If there are a few competitors that have achieved clear rounds (ie. no faults) then there will be a jump-off in which there will be a tough course made and your aim then is to jump clear and quick. The person with the least faults and quickest time will then be in the lead for the showjumping phase.