The standard dressage arena letters are A-K-V-E-S-H-C-M-R-B-P-F.
The letters on the long sides of the arena, nearest the corners, are 6 m (20 ft) in from the corners, and are 12 m (39 ft) apart from each other.
The most accomplished horse and rider teams perform FEI tests, written by the international equestrian governing body called the Fédération Équestre Internationale or FEI.
The highest level of modern competition is at the Grand Prix level.
For example, the horse's straightness going across the diagonal may be assessed by judges at M and H.
Although the judge's positions are known by their closest letter, only C, B, & E are actually directly behind their respective marker, with the other judges being on the short sides (on a plane with C, and two metres in from the edge of the arena for M & H, and at the A end of the arena and five metres in from the long side of the arena for F & K) rather than on the longside where the letter would seem to indicate.
As well as the center line, the arena also has two "quarter lines" which lie between the center line and the long side of the arena, however these are infrequently, if ever, used for competition except in a freestyle.
The most popular horse breeds seen at the Olympics and other international FEI competitions are warmblood horses bred for dressage.
In classical dressage training and performances that involve the "airs above the ground" (described below), the "baroque" breeds of horses are popular and purposely bred for these specialties. Each has letters assigned to positions around the arena for dressage tests to specify where movements are to be performed.
Cones with letters on them are positioned on the sidelines of the arena for reference as to where a movement is to be performed.
The small arena is 20 by 40 m (66 by 131 ft) and is used for the lower levels of eventing in the dressage phase, as well as for some pure dressage competitions at lower levels.