Complex sentence: The Normans invaded and began to colonise the area in 1067-91, although conflict with the Welsh continued intermittently until 1217, when William Marshal sent troops to retake the castle at Caerleon from the Welsh.
Split into simpler sentences: The Normans invaded and began to colonise the area in 1067-91, although conflict with the Welsh continued intermittently until the early 13th century. In 1217, William Marshal sent troops to retake the castle at Caerleon from the Welsh.