The Neapolitan Mastiff Italian Mastiff (Mastino Napoletano in Italian) is a large ancient dog breed. This massive breed is often used as a guard and defender of family and property due to their protective instincts and their fearsome appearance. The breed is reported to have been used to fight alongside the Roman Legions by having bladed and spiked leather harnesses tied to their backs and being trained to run under the bellies of enemy horses to disembowel them.