These keeps, built mainly for security, have but few external openings, and those rarely of any size. Sometimes the narrowest part of the loop is in the centre of the wall, with a splay each way, having the section of an hour-glass. This is seen at Kenilworth and Porchester, late keeps. The arrangement seems a bad one, much aiding the entrance of an arrow. The larger windows, sometimes of 3 ft. or 4 ft. opening, were closed with shutters. A well was an important accessory to a Norman keep. In Dover there are two—one being in the forebuilding. Sometimes, as at Bamburgh and Castle Rising, its mouth is at the ground level. More frequently its pipe is contained within the wall, and opens into a special well-chamber, as at Dover, Newcastle, and Kenilworth. At Carlisle it is in the wall, and was reached by an internal lateral opening, now converted into an external one. At Rochester it is in the cross-wall; the pipe there ascends to the summit, and has an opening at each floor, and there are traces of some such arrangement at Canterbury. At Porchester the well occupies one angle of the wall, and opens on each floor. At Colchester the well, long closed, has been discovered. It is in the basement, near the entrance. At Hedingham there is known to be a well, but its place is lost. At Bamburgh, one of the most remarkable wells in the country, carried down 145 ft. in whin rock, was only discovered in the last century. At Richmond a hollow octagonal pier, carrying the vault, has been built exactly over the well, which is reached through it. At Arques, in Normandy, where the well is near one angle, a pipe has been built over it, raising the mouth to the first floor. At Bowes, Brough, Brougham, Guildford, Castleton, and Corfe, no well has been discovered, and it is only very recently that one has been laid open in the White Tower, in London.