On the building of Château Gaillard, the following account is given by Masseville, in his _History of Normandy_:[185]--"In the year 1196, a few months after the treaty of Louviers had been concluded between Philip-Augustus and Richard Coeur-de-Lion, the Norman Duke, considering how frequently inroads had been made into his territories, by the way of Andelys, resolved to strengthen himself by means of a formidable barrier in that quarter. With this view, he built a fortress upon an island in the Seine, opposite the village of Lesser Andelys; and, at the same time, erected upon the brow of the rock that overhung the river, a castle of the greatest possible strength, without, however, reflecting how far these works were likely to affect the rights, or to diminish the revenues, of the see of Rouen, to whom the ground belonged. But Walter, who then wore the archiepiscopal mitre, was by no means of a character patiently to submit to an invasion of his privileges. He complained loudly during the progress of the works, menaced the artificers, and even the prince himself, with the vengeance of the church; and, finally, finding his threats and his remonstrances equally disregarded, had recourse to the bold measure of laying the whole of Normandy under a spiritual interdict. The king, alarmed at so decisive a step, appealed to the papal see, and sent the bishops of Durham and of Lisieux, as his ambassadors to Rome. The archbishop also repaired thither to plead his own cause; and the affair was finally compromised by an exchange, in virtue of which, the castles were allowed to stand, and the secular seigniory of Andelys was ceded to the duke, who, in return for this acquisition, and to obtain his reconciliation to the church, gave up to the primate the towns and lordships of Dieppe and Louviers, the land and forest of Alihermont, the land and lordship of Bouteilles, and the mills of Rouen."--The contract was considered of so much importance, that the archbishop of Canterbury, together with several other English prelates, as well as almost all those of Normandy, and many of the principal abbots and noblemen of the province, were summoned to sanction the execution of it by their presence. Such were the benefits it was supposed to bestow upon the church, that it has passed in ecclesiastical history, under the significant appellation of the _celebris permutatio_.