From Horse

Breeding the Azteca began in 1972 by crossing the Andalusian and American Quarter Horse, and some crosses were made between Andalusian stallions and Criollo mares. Early on, some of the leading breeders realized that systematic, scientific breeding was necessary and that the whole process would require a demanding inspection system. Allowing individual breeders to operate completely on their own produced such a variety of types of offspring that there were an insufficient number of common denominators on which to base a new horse breed.