In the course of the thirteenth century, especially towards its end and notably, as it happened, in the reign of Edward 1 (1272–1307), the castle in England and Wales achieved in architectural terms its apogee. That there could be particular reasons beyond mere architectural logic for these developments will be noted later as appropriate, but meanwhile it is beyond dispute that a concurrence of circumstances produced, at the turn of the thirteenth and fourteenth centuries, the castles, for example, of Caernarvon (21, XIII) and Conway (22, XIV), Harlech (23, XV), Beaumaris (24, XVI) and Caerphilly (26, XX), which are not only the finest and noblest in Britain but also amongst the finest and noblest in Western Europe and Latin Christendom. The principles of their construction, above all the flanking tower and gate-tower, were not new but manifest a century earlier at Dover or Chaˆteau-Gaillard, and going back, whether in stone or timber, far beyond and probably to the beginning. But they are applied and developed in this period with a sophistication and ruthless confidence that beggars all description. By these means the castle is now bound, as it were, into an integrated unit, its whole enceinte adequately, and aggressively, defended, sometimes tailored to the living rock on which it stands (Goodrich, Conway), or, when the chosen site has no such natural advantages, doubly secured by concentric fortification (Beaumaris, Caerphilly), and/or set within a great expanse of water (Leeds in Kent, Kenilworth, or Caerphilly again, which has both the last named defences).

The result, in many of the new or redeveloped castles of the age, which opens, so to speak, with Beeston and Bolingbroke, both new castles built by Ranulf de Blundeville, earl of Chester, in the 1220s, and ends with Edward's Beaumaris, is often the enclosure type of castle with no keep or great tower as pièce maîtresse to provide both ultimate military strong-point and the best residential accommodation. Since also such castles are, perhaps misleadingly, commonly regarded as particularly characteristic of the period, it may seem that the keep has gone out of fashion, rendered unnecessary by the developed strength of the enclosure and the increasingly sumptuous residential accommodation within it.