The third struggle was between 1277 and 1282. The rule of the new officials drove the Welsh to revolt; and the chiefs who had opposed Llywelyn, especially his brother David, begged for Llywelyn's protection. Eleanor, Llywelyn's wife and Edward's cousin, tried to keep the peace, but she died while they were arming for the last bitter war of 1282.
It was comparatively easy for Edward to overrun Powys or Deheubarth,if he had an army strong enough. But at that time Gwynedd was almost impregnable. From Conway to Harlech lies the vast mass of Snowdon, a great natural rampart running from sea to sea. Its steep side is towards the east, and the invader found before him heights which he could not climb, and round which he could not pass. If you stand in the Vale of Conway, look at the hills on the Arvon side—the great natural wall of inmost Gwynedd, with its last tower, the Penmaen Mawr, rising right from the sea. The gentle slopes are to the west,and there the corn and flocks were safe.
Edward had to put a large army into the field, and it cost him much.In the war with Llywelyn he had to change the English army entirely; and, in order to get
