Tibetan Mastiff dog breed belong to an ancient stock. It is believed that at least most of all mastiffs descend from that old Tibetan stock. Tibetan Mastiffs is very large. They were once used to guard the holy city of Lhasa and even now those few that remain in Tibet still make excellent guard dogs. The breed began to die out in Tibet during the 19th century until English breeders took them home and bred them. Even now they are still rare. English Mastiffs are quite gentle.