The name for the Spanish mastiff in Spain is Mastn Espao. People kept this big dog because it was strong and skillful and it offered good service as a guard dog as shepherds took care of sheep in the grazing areas. The Spanish mastiff is also brave and has a good reputation of defending and protecting livestock from predators such as wolves and others that harm herds of livestock.

It is commonly thought that the Spanish mastiff is a descendent of the Greek dogs that were introduced to Spain in 1000 BC. These dogs were mainly introduced by the Phoenician and Greek Marine traders who frequented the Iberian Peninsula in that time. The Greeks were noted for utilizing similar dogs for their large size and strength during warfare and battles.

While the conquest of South and North America went on, the people of Spain employed the Spanish mastiff and other Molossers in their warfare against North American tribes like the Mayans and Aztecs among other tribes. Since these dogs were strong, fierce and trained for combat, the native Indians feared them.

Visually, the Spanish mastiff seems to be an awesome, huge animal. Its appearance is much like that of other breeds of mastiff and its head is big with loose folded skin in addition to the common double dewlap on its neck.

The wither height of male Spanish mastiffs is usually up to thirty inches. Their weight averages between 110 to 140 pounds. Female Spanish mastiffs can attain the height of 28 inches and they weigh between 110 to 130 pounds typically. However, it is common to find huge Spanish mastiffs, which are double this size.

The muzzle of the Spanish mastiff is longer in comparison with that of other mastiffs. Besides that it has drop ears that are in the shape of triangles and very small eyes. The typical color of the coat is fawn or reddish but it can also range towards black, brindle and the color of a wolf's fur coat. The woolly texture of the fur keeps the dog warm along with the dense layer underneath.

This dog is stocky and powerful with a chest that looks like that of a very heavy animal. The dog has a rectangular body with strong muscles and strong, heavy bones. On its hind feet, it has a pair of dewclaws just like those found in the Great Pyrenees breed. The tail of the Spanish mastiff is low with a fringed texture. Although this dog is huge, it moves in a smooth and agile manner.

There are basically two types of Spanish mastiff one which is the heavy mastiff and the other that is the light mastiff called Mastin Pesado and Mastin Ligero in Spanish.

The mastiff that weighs more is the type of mountain dog from the northern area of Spain and since this dog is very attractive, it serves as a show dog. The mastiff with less weight is agile and runs faster and you can find it in the southern region of Spain. These mastiffs are not regarded as two different breeds but rather as regional breeds which are slightly different from the other Spanish mastiff.