Man's relationship with the Horse began many millennia ago. The practice of riding horses is estimated at having begun between 6000 and 4000 BC. However dressage as a considered approach to training horses for riding began with the Ancient Greeks, in particular the Athenian Cavalry Commander Xenephon, who is responsible for the first recorded writings on dressage training. He wrote his treatise 'on the Art of Horsemanship' in 360 BC. So dressage training has its origins firmly in the military use of horses, to make them more maneuverable and obedient in battle, also to improve their strength, stamina and agility. The Ancient Greeks approach to training the horse was continued by the Romans, for whom the horse was also a crucial part of their military power. Its fundamental purpose is to develop, through standardized progressive training methods, a horse's natural athletic ability and willingness to perform, thereby maximizing its potential as a riding horse. At the peak of a dressage horse's gymnastic development, the horse will smoothly respond to a skilled rider's minimal aids. The rider will appear relaxed and effort-free while the horse performs the requested movement. Dressage is occasionally referred to as "Horse Ballet". With the increasing popularity of indoor riding practiced by the royalty and nobility, dressage training started to become an art in its own right, with the development of the dressage movements, such as lateral work, piaffe, passage, and airs above the ground (the levade, courbette and so on). At this time dressage training started to become a much more refined activity than the standard training of horses for the military. Although the discipline has ancient roots, dressage was first recognized as an important equestrian pursuit in Europe during the Renaissance.