Rathlin Island , 5 sq mi (13 sq km), Moyle dist., N Northern Ireland. Its cliffs, of limestone and basalt, rise at Slieveacarn to 449 ft (137 m). Farming and fishing are important. St. Columba is said to have founded a church there in the 6th cent., and the ruins of a castle in which Robert I (Robert the Bruce) is reputed to have hidden still remain.