In early September 1066, Harald invaded northern England with a fleet of 300 ships and about 15000 men. He was assisted by the estranged and exiled brother of Harold Godwinson, Tostig Godwinson. Initially the Norwegian invaders were successful and were able to capture the city of York.

The army of Harold Godwinson was rushed to the north of the country to battle the invaders. A fierce battle took place at Stamford Bridge on 16th September 1066, and the Norwegian invaders suffered a crushing defeat. King Harald of Norway was killed in the battle.  Out of the 300 ships that had reached England, only 24 could return with the injured warriors.

Though the English army was victorious in the battle of Stamford Bridge, it also suffered losses. It was in a battered and weakened state which adversely affected its capacity to repel the Norman  invasion of England.