The Grand National fences are the most famous obstacles throughout horse racing.
The combination of the supreme test of stamina and the difficult fences contributes to one of the most difficult races in the racing calendar.
Here is everything you need to know about The Chair, Becher's Brook, Foinavon and more.
The four-mile, two-and-a-half furlong race consists of 30 fences for horses to navigate, with 16 different fences across Aintree Racecourse.
Some of the obstacles in the Grand National are the minimum height for National Hunt fences in the UK, while The Chair is the biggest Grand National fence at five foot, two inches.
14 of 16 the Grand National fences are taken twice throughout the race.
The fences that are jumped twice are the first 14 fences on the course.
The likes of Becher’s Brook, Foinavon and Valentine's Brook are jumped twice in the Grand National.
The only two fences that are not jumped twice in the Grand National are The Chair and the Water Jump.
Becher's Brook, which is fence six and fence 22 at Aintree, is one of the most famous Grand National fences.
The four foot, 10 inches fence has a drop of 15 centimetres on the landing side, which places the emphasis on jockeys to ensure that their horse doesn't land too steeply.
The fence is named after Captain Becher, who fell at the same fence in his first Grand National and subsequently hid in the water as others jumped over him.
Another of the famous Grand National fences is Foinavon, named after the winner of the 1967 race at odds of 100/1.
The name Foinavon was chosen after a monumental pile-up in the 1967 race which allowed the horse to come from seemingly nowhere to win the race.
The tallest and most daunting of the fences is The Chair, which was named after the judge who determined the distances between Grand National horses and used to sit parallel to the fence.
With a 15 centimetre rise on the landing side and a 1.83 metre ditch in front of The Chair, it provides a difficult test for horses every year.
Other famous fences at the Grand National include the Canal Turn and Valentine's Brook.