Besides any other approaches, it is evident that the curtain was always made use of as one way to the keep, and at Arundel and Tamworth is still so used, the parapet in front and rear protecting the rampart walk. As, however, it was a fundamental rule in Norman castles that the keep, the final retreat, however many its approaches, should have as few entrances as possible, the curtain usually stopped at the top level of the mound, and was continued only as a parapet, so that those who came along the wall had, on reaching the keep, to pass along its outside a greater or less distance before they reached the doorway. This is well seen at Tamworth. At Arundel the wall is raised to the full height of the keep, as at Lincoln, but this is not usual. At Hawarden the curtain is continued 10 feet or 12 feet high, and so abuts upon the keep, but the rampart walk does not communicate with it. The position of the well in these keeps has already been noticed. At York and Tickhill it is within the area. That at Arundel is in a tower outside the wall, but a part of it. That at Berkeley is also in a tower, a part of the wall. Those of Alnwick and Kilpeck are in the wall itself; those of Cardiff and Wallingford at the foot of the mound, just within the ditch. It is much to be regretted that so few of these shell keeps remain, even in ruin, and very few, indeed, in a state at all approaching to their original condition, for, as the representatives of a very early form of fortification, and as the chief seats of very ancient estates, and of original English families, they possess a very peculiar interest. Nor are they, when of large size, at all wanting in a noble effect. It is true that upon level ground, as that occupied by the Tower of London, or upon such a ridge as Corfe, or such an elevated platform as Hedingham, the rectangular keep produces a very fine effect, but there are positions in which this is fully equalled by the keeps of the other type. At Durham, where the central tower of the cathedral is equal in grandeur and simplicity to a rectangular keep, it is eclipsed by the adjacent castle. The keep of Belvoir, which, though rebuilt and weak in its details, retains its original outline, would be ill exchanged for the towers even of Norham or Lancaster, and no other structure could be substituted to advantage for the keep of Windsor, crowning and completing its “tiara of proud towers.” Massive as is the rectangular keep, simple, uncompromising, and warlike its features, still, even when seen to its greatest advantage, as on the promontory of Dover or the bold impregnable rock of Bamburgh, it must be confessed to be inferior in grandeur and in completeness of outline to the stern round tower of other days, identified as it is with the early residences of the adventurous Northmen who laid the foundations of the English people. LIST (APPROXIMATIVE) OF SHELL KEEPS, PAST OR PRESENT.