Duchy of Normandy

The Duchy of Normandy grew out of the 911 Treaty of Saint-Clair-sur-Epte between King Charles III of West Francia and the Viking leader Rollo. The duchy was named for its inhabitants, the Normans.

From 1066 until 1204, as a result of the Norman Conquest of England, the dukes of Normandy were usually also kings of England, the only exceptions being Dukes Robert Curthose (1087–1106), Geoffrey Plantagenet (1144–1150), and Henry II (1150–1152), who became king of England in 1154.

In 1202, Philip II of France declared Normandy forfeit to him and seized it by force of arms in 1204. It remained disputed territory until the Treaty of Paris of 1259, when the English sovereign ceded his claim except for the Channel Islands. With the mainland portions of the Duchy absorbed into the French Royal Domain, the now much smaller Duchy continued to exist under the authority of the English sovereign until it was split into the Bailiwicks of Guernsey and Jersey around 1290 by Otto de Grandson.

In the Kingdom of France, the duchy was occasionally set apart as an appanage to be ruled by a member of the royal family. After 1469, however, it was permanently united to the royal domain, although the title was occasionally conferred as an honorific upon junior members of the royal family. The last French duke of Normandy in this sense was Louis-Charles, duke from 1785 to 1792.

The title "Duke of Normandy" continues to be used in an informal manner in the Channel Islands, to refer to the monarch of the United Kingdom. There is no definite end as to when the Duchy of Normandy (with its remnants in the Channel Islands) as a vassal of the English monarch became 'part' of the United Kingdom, with history blending the link between the two gradually. In official documents in Guernsey, the British monarch is entitled "Duke of Normandy", while in official documents in Jersey, the British monarch is ambiguously titled Sovereign.

In 1204, Normandy was transferred from the English Crown to France, with the exception of the Channel Islands, which were never incorporated into England. As such, although no form of the Duchy or its structure exists, there has never been a formal end to Norman state rule over the islands.

The first Viking attack up the Seine river took place in 820. By 911, the area had been raided many times and there were even small Viking settlements on the lower Seine. The text of the Treaty of Saint-Clair-sur-Epte has not survived. It is only known through the historian Dudo of Saint-Quentin, who was writing a century after the event. The exact date of the treaty is unknown, but it was likely in the autumn of 911. By the agreement, Charles III, king of the West Franks, granted to the Viking leader Rollo some lands along the lower Seine that were apparently already under Danish control. Whether Rollo himself was a Dane or a Norwegian is not known. For his part, Rollo agreed to defend the territory from other Vikings and that he and his men would convert to Christianity. Rollo's decision to convert and come to terms with the Franks came in the aftermath of his defeat at the battle of Chartres by Richard of Burgundy and Robert of Neustria (the future Robert I of France) earlier in 911.

The territory ceded to Rollo comprised the pagi of the Caux, Évrecin, Roumois and Talou. This was territory formerly known as the county of Rouen, and which would become Upper Normandy. A royal diploma of 918 confirms the donation of 911, using the verb adnuo ("I grant"). There is no evidence that Rollo owed any service or oath to the king for his lands, nor that there were any legal means for the king to take them back: they were granted outright. Likewise, Rollo does not seem to have been created a count or given comital authority, but later sagas refer to him as Rúðujarl (earl of Rouen).