Following the death of the Welsh king, Rhys ap Tewdwr, in 1093, the Norman baron, Roger de Montgomery invaded the deceased king's lands in south-west Wales and claimed them for himself. He made his base at Pembroke where he built a castle on a rocky promontory between the Pembroke River and the Monkton Pill. Roger's sons lost the castle to the crown following a failed rebellion, and in 1138 the earldom of Pembroke was created and given, along with the castle, to Gilbert de Clare. His son, Richard 'strongbow', used Pembroke as a base from which to launch an invasion of Ireland. On his death in 1176 he held the titles of Earl of Pembroke and Striguil, Lord of Leinster and Justiciar of Ireland. However he died without a male heir and the castle reverted to the crown, who continued to use it as a convenient base from which to monitor royal interests in Ireland.