Castles of the type known as Edwardian or concentric, though taking their name from Edward I., were, as a chronological fact, introduced in the reign of his father, and Caerphilly, one of the earliest, probably the very earliest, of the concentric type, and curiously enough one of the most complete, was constructed by the Lord of Glamorgan in the very last year of Henry’s reign. Caerphilly is second only to Windsor in extent, and second to no mediæval fortress whatever in the skill with which it is laid out, and the natural features of the ground turned to advantage. It was executed, and probably planned, with great rapidity. Its cost must have been enormous, and must have taxed to the utmost the resources of even so wealthy a noble as the Earl of Gloucester and Hertford. The type thus introduced was adopted by Edward I., and is exemplified in the castles of Harlech and Beaumaris. Conway and Caernarvon, though superior in magnificence to these and less symmetrical, are chiefly remarkable because they form a part of the defences of the towns attached to them, the whole being of one date and parts of one plan. The reign of Edward much diminished the value of English castles. Even the fortresses erected by him in North Wales, when their end was attained and the province reduced to subjection, ceased to be of value and gradually fell into decay, and in England when once his rule was established and his power realised, the lords even of the strongest castles did not venture to garrison them against him. CHAPTER IX. THE RECTANGULAR KEEP OF A NORMAN CASTLE. In a preceding chapter an attempt was made to describe the appearance and to give an outline of the history of those earthworks in England and Normandy upon which the Norman and Anglo-Norman barons founded their chief strongholds, and which, therefore, are connected with the military architecture of either country. It is now proposed to describe the buildings themselves, whether placed within the ancient earthworks or altogether of original foundation, which constituted the fortresses of England in the eleventh and twelfth centuries, through the periods known in ecclesiastical architecture as the Norman and Transition, and which, in military architecture, include the Norman form of castle. What is known as the Norman style of architecture prevailed in England from the Conquest to the close of the reign of Stephen,—that is, from 1066 to 1154; but this latter is necessarily an arbitrary date, since it was by degrees only that one style of architecture passed into another, and the Norman features, though found in all buildings, and especially in castles, down to the end of the reign of Henry II., or 1189, became more and more mixed up with those of the succeeding style.