Back to Times Before the Roman Empire
A comparison of Assyrian dogs’ depictions with Roman war dogs’ images would certainly reveal substantial likeness. One may discover that not only shapes of dogs, but also faces of humans are alike. Still, according to specialists’ examination, it’s not the matter of simple outward resemblance: artists of the ancient world produced their images in accordance with canonical samples, so the same generalized images of humans, dogs and other creatures were used by artists for centuries. The art was representing types, not portraits. Thus, none can be certain that huge war dogs on Egyptian and Mesopotamian artwork were Mastiffs’ ancestors. They could be any other indigenous big fighting dog breed.
Moreover, it’s highly improbable that Phoenician traders would transport massive war dogs in their boats. The conditions there were very restrained and living creatures, especially huge war dogs seems to be too risky and fragile merchandise - moreover the one, that needed substantial feeding.