The invasion of Kerry began in 1201, under the leadership of William de Burgh, a great Norman magnate from East Anglia. The military conquest must have been complete by 1206, when the Anglo-Normans built a castle at Dunloe, near Killarney. The kingdom of the Corcu Duibne with its three territories, including Áes Irrais Tuaiscirt, was granted to Geoffrey de Mareis, a powerful Norman lord from Somerset. He built a castle at Killorglin, 30 miles east of Dingle, as his headquarters. He must have driven the O'Connells out of the peninsula, and also became the overlord of the O'Falveys and O'Sheas to the south. The three cantreds established by de Mareis were based on the three territories of the old kingdom of Corcu Duibne. In this way one of these territories, Áes Irrais, became the cantred of Osurrys. Its capital was located at Dingle. De Mareis, who had lands elsewhere in Ireland as well as his Kerry estates, appointed an officer, called a seneschal, to administer Osurrys. De Mareis was viceroy or governor of Ireland several times between 1215 and 1232, though his career ended in disgrace when he was found to be involved in an assassination plot against another Norman lord.
