The principles of defence of the walled town are those of the castle; and hitherto we have drawn illustrations from both with little discrimination. In both cases the same methods of attack are provided against by the use of the same means. But it must be remembered that the area of the town is larger than that of the castle, and that while, in the castle, the bailey is the common muster-ground from which every part of the curtain can be easily reached, there can be no such open space enclosed by the walls of a large inhabited town or city. Thus, while the market-place, in or near the centre of the town, would serve as a general rallying-ground,[301] it was necessary also to keep a clear space at the foot of the inner side of the walls, so that free communication between every part might be preserved. From the continuous lane which was thus formed between the wall and the houses of the town, and was crossed at intervals by the main thoroughfares leading to the gates, access was gained to the rear of the flanking towers, and to the stairs by which, from time to time, the rampart-walk was reached. Most towns which have been walled retain traces of this arrangement. At Southampton the _pomerium_,[302] as this clear space is called in medieval documents, survives on the east side of the town in the lane still known as “Back of the Walls.” At Carnarvon it is nearly entire, except on the west side of the town. At Newcastle (293) it remains in a very perfect state on the north-west side of the enclosure, where the walls and their intermediate turrets are also fairly perfect; and it can be traced in a paved lane on the west side, where the walls are gone.[303] Nearly the whole extent of the inner city walls of Bristol, of which little remains, can be easily traced by the survival of the _pomerium_ in a series of curved lanes. The line of the east wall of Northampton can be recovered in the same way; and although, as at York, modern encroachments have in many places removed the _pomerium_, it usually survived to mark the site of town walls, even long after those walls had been destroyed.