Starting with Rollo, Normandy was ruled by an enduring and long-lived Viking dynasty.
Illegitimacy was not a bar to succession and three of the first six rulers of Normandy were illegitimate sons of concubines.
Rollo's successor, William Longsword managed in expanding his domain and came into conflict with Arnulf of Flanders, who had him assassinated in 942.
This led to a crisis in Normandy, with a minor succeeding as Richard I and also led to a temporary revival of Norse paganism in Normandy.
Richard I's son, Richard II was the first to be styled duke of Normandy, the ducal title becoming established between 987 and 1006.

The Norman dukes created the most powerful, consolidated duchy in Western Europe between the years 980, when the dukes helped place Hugh Capet on the French throne, and 1050.
Scholarly churchmen were brought into Normandy from the Rhineland, and they built and endowed monasteries and supported monastic schools.
thus helping to integrate distant territories into a wider framework.
The dukes imposed heavy feudal burdens on the ecclesiastical fiefs, which supplied the armed knights that enabled the dukes to control the restive lay lords but whose bastards could not inherit.
By the mid-11th century the Duke of Normandy could count on more than 300 armed and mounted knights from his ecclesiastical vassals alone.
By the 1020s the dukes were able to impose vassalage on the lay nobility as well.
Until Richard II, the Norman rulers did not hesitate to call Viking mercenaries for help to get rid of their enemies around Normandy, such as the king of the Francs himself.
Olaf Haraldsson crossed the Channel in such circumstances to support Richard II in the conflict against the count of Chartres and was baptized in Rouen in 1014.

In 1066, Duke William defeated Harold II of England at the Battle of Hastings and was subsequently crowned King of England, through the Norman conquest of England.
Anglo-Norman and French relations became complicated after the Norman Conquest.
The Norman dukes retained control of their holdings in Normandy as vassals owing fealty to the King of France, but they were his equals as kings of England.
From 1154 until 1214, with the creation of the Angevin Empire, the Angevin kings of England controlled half of France and all of England, dwarfing the power of the French king, yet the Angevins were still technically French vassals.

The Duchy remained part of the Anglo-Norman realm until 1204, when Philip II of France conquered the continental lands of the Duchy, which became part of the royal domain.
The English sovereigns continued to claim them until the Treaty of Paris (1259) but in fact kept only the Channel Islands.
Having little confidence in the loyalty of the Normans, Philip installed French administrators and built a powerful fortress, the Château de Rouen, as a symbol of royal power.
Starting with Rollo, Normandy was ruled by an enduring and long-lived Viking dynasty. Illegitimacy was not a bar to succession and three of the first six rulers of Normandy were illegitimate sons of concubines. Rollo's successor, William Longsword managed in expanding his domain and came into conflict with Arnulf of Flanders, who had him assassinated in 942. This led to a crisis in Normandy, with a minor succeeding as Richard I and also led to a temporary revival of Norse paganism in Normandy. Richard I's son, Richard II was the first to be styled duke of Normandy, the ducal title becoming established between 987 and 1006.
The Norman dukes created the most powerful, consolidated duchy in Western Europe between the years 980, when the dukes helped place Hugh Capet on the French throne, and 1050. Scholarly churchmen were brought into Normandy from the Rhineland, and they built and endowed monasteries and supported monastic schools. thus helping to integrate distant territories into a wider framework. The dukes imposed heavy feudal burdens on the ecclesiastical fiefs, which supplied the armed knights that enabled the dukes to control the restive lay lords but whose bastards could not inherit. By the mid-11th century the Duke of Normandy could count on more than 300 armed and mounted knights from his ecclesiastical vassals alone. By the 1020s the dukes were able to impose vassalage on the lay nobility as well. Until Richard II, the Norman rulers did not hesitate to call Viking mercenaries for help to get rid of their enemies around Normandy, such as the king of the Francs himself. Olaf Haraldsson crossed the Channel in such circumstances to support Richard II in the conflict against the count of Chartres and was baptized in Rouen in 1014.
In 1066, Duke William defeated Harold II of England at the Battle of Hastings and was subsequently crowned King of England, through the Norman conquest of England. Anglo-Norman and French relations became complicated after the Norman Conquest. The Norman dukes retained control of their holdings in Normandy as vassals owing fealty to the King of France, but they were his equals as kings of England. From 1154 until 1214, with the creation of the Angevin Empire, the Angevin kings of England controlled half of France and all of England, dwarfing the power of the French king, yet the Angevins were still technically French vassals.
The Duchy remained part of the Anglo-Norman realm until 1204, when Philip II of France conquered the continental lands of the Duchy, which became part of the royal domain. The English sovereigns continued to claim them until the Treaty of Paris (1259) but in fact kept only the Channel Islands. Having little confidence in the loyalty of the Normans, Philip installed French administrators and built a powerful fortress, the Château de Rouen, as a symbol of royal power.
Duchy of Normandy