Viking invasions began in the 9th century, followed by more permanent settlements, particularly along the east coast of Ireland, the west coast of modern-day Scotland and the Isle of Man. Though the Vikings were eventually neutralised in Ireland, their influence remained in the cities of Dublin, Cork, Limerick, Waterford and Wexford. England however was slowly conquered around the turn of the first millennium AD, and eventually became a feudal possession of Denmark. The relations between the descendants of Vikings in England and counterparts in Normandy, in northern France, lay at the heart of a series of events that led to the Norman conquest of England in 1066. The remnants of the Duchy of Normandy, which conquered England, remain associated to the English Crown as the Channel Islands to this day. A century later the marriage of the future Henry II of England to Eleanor of Aquitaine created the Angevin Empire, partially under the French Crown. At the invitation of a provincial king and under the authority of Pope Adrian IV (the only Englishman to be elected pope), the Angevins invaded Ireland in 1169. Though initially intended to be kept as an independent kingdom, the failure of the Irish High King to ensure the terms of the Treaty of Windsor led Henry II, as King of England, to rule as effective monarch under the title of Lord of Ireland. This title was granted to his younger son but when Henry's heir unexpectedly died the title of King of England and Lord of Ireland became entwined in one person.