King John's Castle (Irish: Caisleán Luimnigh) is a 13th-century castle located on King's Island in Limerick, Ireland, next to the River Shannon. Although the site dates back to 922 when the Vikings lived on the Island, the castle itself was built on the orders of King John in 1200. One of the best preserved Norman castles in Europe, the walls, towers and fortifications remain today and are visitor attractions.