It was during this period that machicoulis and alurs reached their highest efficiency and development, and in every castle built after 1250 they may be found wherever extra strengthening of the defence was desirable. In some illustrated medieval romances of the second part of the thirteenth century the castle is depicted with these additions, although at times the perspective indulged in by the artist is somewhat disconcerting. Where machicolation was not adopted, probably by reason of the expense, the walls were generally corbelled outwards at the upper parts of towers and walls, thus giving a more effective control over the bases of these structures where mining or battering might be attempted. Battlementing was almost universal, and the system of piercing the merlons with arbalestraria may be assigned to this early date, although not reaching the full development it subsequently met with in the Edwardian Castles of Wales. It may be seen in illustrated manuscripts in the form of simple circular openings in the merlons. The protection of loopholes and windows by a hanging shield is likewise illustrated; it prevented the admission of arrows and bolts discharged with a high trajectory. The maximum development of the art of castle-building in the British Isles occurred in the reign of Edward I. and is exhibited in its best form in those magnificent buildings which he erected in Wales to consolidate the conquest of that country. With the great Snowdonian range as the centre he placed a ring of fortresses at those strategic points, chosen with remarkable military perspicacity, where they would be of the utmost advantage in commanding the widest stretch of country. Criccieth and Harlech, standing upon the sites of previous strongholds, and Conway and Carnarvon upon entirely new ground, are the most prominent and famous of this encircling ring. The term "Edwardian," however, for a Concentric Castle so frequently used, is a misnomer, because some of the grandest examples of the style date from the time of Henry III.; the outer ward of the Tower of London, for example, rendered it concentric in 1240 to 1258.