The brunt of the war fell on Normandy and ultimately on the castles which supplied the duchy’s lack of natural frontiers. To supplement the great interior fortresses of Caen, Falaise, Argentan, Montfort, and Rouen, Henry I began the organization of a series of fortifications on the southern and eastern borders. Henry II, we are told, improved or renewed nearly all these strongholds, and especially Gisors, the frontier gateway toward France, on which fortress the exchequer roll shows him expending 2650 pounds Angevin in a single year. These castles, remains of many of which are still standing, were typical of the best military architecture of their age, but they were inferior in strength and scientific construction to the great fortresses of Christian Syria, such as Krak or Margat, which seem to have gone back to Byzantine and even Persian models. A keen warrior like Richard had not spent his two years in Palestine without gaining an expert knowledge of eastern methods in the art of war, and we are not surprised to find that he had Saracen soldiers and Syrian artillerymen with him in his Norman campaigns, and that he made large use of oriental experience in strengthening his defences. His masterpiece, of course, was Château Gaillard, the saucy castle on the Seine controlling the passage of the river and its tributaries in that region of the Norman Vexin which was the great bone of contention between the Plantagenets and the French kings. Having first expropriated at great expense the lord of the region, the archbishop of Rouen, he fortified the adjacent island of Andeli and laid out a new town on the bank. This he surrounded with water and reënforced with towers and battlements, protecting the whole with a stockade across the river and outlying works farther up. Then on the great rock above he built the fortress, with its triangular advance work, its elliptical citadel, and its circular keep surrounded by a “_fossé_ cut almost vertically out of the rock.” There was no dead angle, such as permitted sappers to reach the base of rectilinear walls, but instead a sloping base down which projectiles might ricochet; nor was there, as at the corners of square towers, any part of the surrounding area which could not be reached by direct fire from within. “The approaches and the _fossé_,” says Dieulafoy,[45] “were covered by the fire of the garrison right up to the foot of the scarp, and no sapper could touch any point in towers or walls, provided that the fortress was under the direction of an experienced commander.” This qualification is important, for the new type of fortification was designed for an active defence, one might almost say an offensive defence, and not for the mere passive resistance with which the older strategy had been content. The works at Andeli, carried on largely under Richard’s personal direction, occupied more than a year of labor and cost nearly 50,000 pounds Angevin, which