The Neapolitan Mastiff is a large size dog. It was originally bred to be a very versatile dog. It was used to be a herder, guard dog, hunter and companion dog. The Neapolitan Mastiff can grow to a height of 30 inches and weigh up to 150 pounds. It is a strong dog that is protective. Even with it's size, it's a calm dog that does not require a large amount of activity.