The English Mastiff, or simply the Mastiff, is a British dog breed of very large size. It is likely descended from the ancient Alaunt and Pugnaces Britanniae, with a significant input from the Alpine Mastiff in the 19th century. Distinguished by its enormous size, massive head, short coat in a limited range of colours, and always displaying a black mask, the Mastiff is noted for its gentle and loving nature. The lineage of modern dogs can be traced back to the early 19th century, but the modern type was stabilised in the 1880s and refined since. Following a period of sharp decline, the Mastiff has increased its worldwide popularity. Throughout its history the Mastiff has contributed to the development of a number of dog breeds, some generally known as mastiff-type dogs or, confusingly, just as "mastiffs". It is the largest living canine, outweighing the wolf by up to 50 kg (110 lbs) on average.

Dogs of Roman Britain concerns the presence of dogs within Britain under Roman occupation. Through various excavations in the Province of Britannia, evidence for a variety of uses from dogs has been found. There has been evidence of cultural involvement and significance of dogs found among the remains of excavated sites. Along with this are written references to the use of dogs as well.