The Carboniferous Limestone island rises to about and serves as a wind and wave break, sheltering the upper reaches of the Bristol Channel. The island is now uninhabited, with the exception of the wardens. It is protected as a nature reserve and Site of Special Scientific Interest (SSSI) with a large bird population and plants including wild peonies. There was a signal station or watchtower on the island in Roman times, but there may have been human habitation as early as the Iron Age. In the 6th century it was home to St Gildas and to a small Augustinian priory in the 12th and 13th centuries. An inn was built in 1832 and used for holidays in the 19th century. A bird sanctuary was established in 1931 and since 1951 has been leased to charitable trusts. It is now owned by the Kenneth Allsop Memorial Trust.