The Battle of Stamford Bridge took place at the village of Stamford Bridge, East Riding of Yorkshire in England on September 25, 1066, shortly after an invading Norwegian army under King Harald Hardrada (Haraldr harðráði) defeated the army of the northern earls Edwin of Mercia and Morcar of Northumbria at the Battle of Fulford two miles south of Jorvik. After a lengthy forced march up to Stamford Bridge that took place in just four days, King Harold Godwinson of England caught Harald's force by surprise, which meant that the soldiers were unarmoured. After a stubborn battle, the majority of the Norwegians were killed along with Harald Hardråda and Earl Tostig, Harold's brother.
In September 1066, King Harold Godwinson was in the south of Britain, anticipating an invasion from Normandy by William the Conqueror. By coincidence, Harald Hardråda King of Norway, and Tostig (the expelled Earl of Northumberland) landed in England and burned Scarborough. Harald Hardråda was pursuing dynastic claims with an army of Norwegians, Norwegian vassals, and allies, with the intent of conquest of England, rather than raiding. King Harold Godwinson and his brother Gyrth set out with their Housecarls and royal Thegns for Yorkshire to repel the Viking invasion. After Harold learned that Northumbrians were told to bring additional supplies and hostages to the Vikings at Stamford Bridge, Harold took his army to Stamford Bridge, where he hoped to surprise the Vikings. When Harold's forces came over the ridge, the Vikings were unarmoured, since they were only expecting a hand over of supplies and hostages.
After marching approximately 180 miles in 4 days, the English army arrived on the west side of the river. Despite being very tired, they were still ready to fight a long and bloody battle. The Viking army could not have been in a more disastrous position. They had expected the Saxons to come up a few days later, and so they were not wearing any armour, as they had left them on their ships. Moreover, their army was split in two by the river and had not placed any kind of defensive measures, such as lookouts.
The Vikings on the west side either put up a futile defence or ran for their lives across the bridge. Those who decided to fight were slaughtered without mercy. However, the Saxons came across an obstacle on the bridge. The story goes that a giant Norseman armed with an axe held up the entire Saxon army, and single-handedly cut down over 40 Saxon soldiers. He himself was only killed when one Saxon drifted under the bridge in a barrel and thrust his spear through the latches of the bridge, killing the Norseman.
Whatever happened, this delay had allowed the Vikings to form something of a line to face the Saxon army. Harold's army poured across the bridge, forming a line face-to-face with the Vikings. The Vikings who were without armour locked their shields together to form a wall. The Saxons copied the tactic and rushed the Viking army. The battle continued for several hours, and though the Vikings put up an impressive defence, without their armour they were exposed to Saxon steel. Chinks began to appear in the shield wall and the Saxons were quick to exploit these gaps. The Saxon army broke up the Viking shield wall, spilled around the rear of their army and continued to fight till the Vikings broke and ran. The Viking leaders were killed, and their army had been almost completely annihilated. The Saxons had won.
King Harold Godwinson accepted a truce with the surviving Norwegians, including Harald's son Olaf, and they were allowed to leave after giving pledges not to attack England again, thus marking the end of the Viking Age.
King Harold's success did not last, however. Little more than a fortnight after the battle, on October 14, after having marched his army all the way from Yorkshire, he was defeated and killed by Norman forces under William the Conqueror at the Battle of Hastings. This began the Norman Conquest of England.