Normandy was a region in the northern part of France, just across the English channel. In 911, the Viking, Rollo settled in this region after an agreement with the king of France. He was expected to protect the region from further Viking attacks.Normandy was a feudal state, where the vassals held land in return for military service.
In 1066, the Duchy of Normandy was ruled by Duke William who also though he had a right to the throne of England . He had been assembling an army to invade England, which also included contingents from other parts of France like Britanny and Flanders.
Soon after the battle of Stamford Bridge got over, Duke William and his army crossed the English channel and landed in England on September 28, 1066 A.D.
On hearing the news of the Norman army landing on the English coast, Harold Godwinson marched south with his army to battle the Norman invaders. He halted briefly at London, to gather more people. This was a strategic mistake as his army was tired and could not match the Norman invaders at the battle of Hastings.