Separate buildings like towers there probably have been in many times and places, and they may have been used as fortresses. Along the Roman Wall were the square towers called mile-castles, which are interesting, not only as the best remains of the arrangements made by the great aggressors for the protection of their frontier, but as the models on which the ancient inhabitants would probably build their castles—if they built any. It is singular enough that the Border peel towers—built a thousand years after the Romans had abandoned Britain to her fate—have, in their compact squareness, more resemblance to these castella, than any type of earlier British castellated architecture possesses. Since the publication of Mr Bruce’s book on the Roman Wall, to which we lately had occasion to refer, no one need remain ignorant of any feature, however minute, which, now existing, attests what these mile-castles originally were. Mr Bruce tells us, in a summary description, that “they derive their modern name from the circumstance of their being usually placed at the distance of a Roman mile from each other. They were quadrangular buildings, differing somewhat in size, but usually measuring from sixty to seventy feet in each direction. With two exceptions, they have been placed against the southern face of the wall: the castle of Portgate, every trace of which is now obliterated, and another near Æsica, the foundations of which may with some difficulty still be traced, seem to have projected equally to the north and south of the wall. Though generally placed about seven furlongs from each other, the nature of the ground, independently of distance, has frequently determined the spot of their location. Whenever the wall has had occasion to traverse a river or a mountain pass, a mile-castle has uniformly been placed on the one side or other to guard the defile. The mile-towers have generally had but one gate of entrance, which was of very substantial masonry, and was uniformly placed in the centre of the south wall: the most perfect specimen now remaining, however, has a northern as well as a southern gateway. It is not easy to conjecture what were the internal arrangements of these buildings—probably they afforded little accommodation, beyond what their four strong walls and well-barred gates gave.”[21] They were evidently mere barracks or stations, nor can much more be said for any of the Roman works in the lands of their conquests. Roman troops were taught, in the conflict with the barbarian, to look solely to discipline; and the places called forts, apart from these square towers along the wall, were merely intrenched camps.