Perched high above the River Seine, an important transport route, the site of Château Gaillard, in the manor of Andeli, was identified as a naturally defensible position. In the valley below the site was the town of Grand Andely. Under the terms of the Treaty of Louviers (January 1196) between Richard and Philip II neither king was allowed to fortify the site; despite this, Richard intended to build a castle at "Andeli". Its purpose was to protect the duchy of Normandy from Philip II—it helped fill a gap in the Norman defences left by the fall of Château de Gisors and above all Château de Gaillon, a castle which belonged to Philip and used as an advanced French fortification to block the Seine valley—and to act as a base from which Richard could launch his campaign to take back the Norman Vexin from French control. Indeed, Les Andelys is located just in front of Gaillon on the other side of the Seine valley. Richard tried to obtain the manor through negotiation. Walter de Coutances, Archbishop of Rouen, was reluctant to sell the manor as it was one of the diocese's most profitable, and other lands belonging to the diocese had recently been damaged by war. When Philip besieged Aumale in northern Normandy, on the border with Picardy, Richard grew tired of waiting and seized the manor, although the act was opposed by the Church.