The walls around coastal cities, such as Southampton, had evolved from simpler Norman fortifications by the start of the 13th century. Later, King Edward I was a prolific castle builder and sites such as Conwy Castle, built 1283 to 1289, defend river approaches as well as the surrounding land. Built 1539 to 1544, the Device Forts are a series of artillery fortifications built for Henry VIII to defend the southern coast of England. Between 1804 and 1812 the British authorities built a chain of towers known as Martello Towers to defend the south and east coast of England, Ireland, Jersey and Guernsey against possible invasion from France. This type of tower was also used elsewhere in the British Empire and in the United States.