Ardglass was an important seaport in post-medieval times, whose defence depended upon a ring of fortified merchants' houses. The largest of these is 15th-century Jordan's Castle overlooking the harbour. Little is known of its history except that it withstood a lengthy siege during the Tyrone Rebellion, when Simon Jordan defended his castle for three years until relieved by Mountjoy in 1601. It probably remained a dwelling until the 17th century, but was a ruin when purchased by the antiquarian F.J. Bigger in 1911, who restored it and bequeathed it to the State in 1926.Near Ardglass Harbour. NGR: J 560372.