We possess a most complete instance of such an arrangement (though without a clerestory), in the chapel of the Tower of London,[24] where this space is made a gallery, covered with a wagon-vault and opens by a second tier of arches into the nave, which is itself covered by a similar vault. Had clerestory windows been in this case desired, the only change requisite would have been to groin the central space and the gallery, instead of giving them plain vaults, and we should then, with a trifle more height, have had a model, on a small scale, of the perfected arrangement of a vaulted and aisled church. Most, however, of our Norman churches in England are imperfect in two particulars as compared with this ideal. They have no groining to the central space, nor any vaulting to the gallery over the aisle. Several, as Durham and Lindisfarne, had the former, and Gloucester, and perhaps Tewkesbury, the latter; but I know of no existing church in England, nor of any perhaps of very early date, even in Normandy, which has both. The Tower chapel is the nearest approach; and, strange to say, the pre-conquestal example at Westminster appears (if I read the description aright) to have had all these features complete, the central space being vaulted, and the aisle also vaulted in two storeys. Such was often the case in Central France, even at an early date, as we see in the Church of St. Stephen at Nevers, erected about 1063, where we find groined aisles, aisle-galleries with the demi-vault, a clerestory, and above it a wagon-vault to the nave. The churches at Nôtre Dame du Pont at Clermont, Issoire, and some others of about the same date in Auvergne, are one point less complete, having all the features I have enumerated excepting only the clerestory: nor do I know that there is any specimen so complete and of early date in Normandy, so that King Edward’s church seems to have gone ahead of its types in Normandy, and its model not to have been reached by its successors in England. Those principles of combination being attained, it was easy to carry them out into a complete building. A nave, such as I have described, may be either continued, with the intervention of a chancel arch, into the choir, and terminated by an apse; or two such ranges of buildings may be made to intersect, the crossing space being surmounted by a central tower, supported on four lofty arches and by massive piers. The east end would usually be terminated by an apse; the cross building, or transept, by gables; and the nave perhaps, by a gable flanked by two towers, which terminated its aisles, or projected beyond them. Transepts may have two aisles, as at Winchester and Ely; one, as at Durham and Peterborough; or none, as at Canterbury, St. Alban’s, and Norwich. In the latter case, apsidal chapels would probably project from its eastern face; and, if the choir aisle runs round the apse, similar chapels may open out of it.