evidence: An ancient Irish monastery at Ferry Hill was destroyed by the Vikings in 841. The Vikings renamed the lough as Kerlingfjörðr ‘narrow sea-inlet of the hag’ but left no physical traces of their presence. This name was copied into Irish as Loch Cairlinne. The next invaders were the descendants of Vikings who had invaded France, creating the territory of Normandy. In the mid eleventh century they invaded England and Wales and then invaded Ireland just over one hundred years later. The Normans set up a ferry service across the lough, which belonged to Inch Abbey, near Downpatrick, and built castles to guard the crossing. Carlingford and Greencastle castles remain imposing ruins to this day. Other castles were built around the lough, including a lost one of the O’Neills, north of Omeath and a motte castle and a fifteenth century tower house near Narrow Water.