Neapolitan Mastiffs, like all European Mastiffs, are derived from Middle Eastern wolves. This evolution likely took several hundred years, and likely involved cross-breeding with other Italian dogs over the centuries. On the surface, it would appear that the Roman gladiator dog would have the same skull and power as a wolf that has to fight moose on a regular basis, the reality is that Neapolitan Mastiffs have not evolved anything like a wolf's skull. 
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A northern wolf evolved to live in a much more intense environment than Rome 's gladiatorial circuses. And there is not a lot of good evidence that suggests that the Neopolitian mastiff is actually the same strain that the Romans used. The type may be old, but the strain most likely has very different genetics now. We do know that much of the Neapolitan Mastiff's features have been exaggerated since it became a show dog, but the wolf can vary only so much in head structure before it becomes unable to take down a moose effectively.
So although it appears that Neapolitan Mastiffs might be closer to wolves in their fighting abilities and phenotype, the two animals are now quite different.
The Neapolitan Mastiff is an estate guard dog from Italy. The breed traces its roots to the dogs of war used by the Roman Army. The breed then existed on estates and farms across Italy for the past two millennia, known as the "big dog of the little man" -- the extraordinary dog of the ordinary man.
While the Neapolitan Mastiff has been recognised as a breed in the modern world only since recognition by the FCI in 1949, we can see, through bas-relief, paintings and statues dating from 3000 years before Christ, that his recorded roots trace to the giant war dogs of Egypt, Persia, Mesopotamia and Asia. Even as grand a figure as Alexander the Great (356-323 BC) was instrumental in creating the modern Neapolitan Mastiff.
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