The Norman expansion into Wales slowed in the 12th century, but remained an ongoing threat to the remaining native rulers. In response the Welsh princes and lords began to build their own castles, usually in wood. There are indications that this may have begun from 1111 onwards under Prince Cadwgan ap Bleddyn with the first documentary evidence of a native Welsh castle being at Cymmer in 1116. These timber castles, including Tomen y Rhodwydd, Tomen y Faerdre and Gaer Penrhôs, were of equivalent quality to the Norman fortifications in the area and it can prove difficult to distinguish the builders of some sites from the archaeological evidence alone. At the end of the 12th century the Welsh rulers began to build castles in stone, primarily in the principality of North Wales.