Harald Hardraada Launches His Invasion
Following the storm on 12 September, which had wrecked parts of Harold's and William's fleets and caused William to abort his first invasion attempt, the wind shifted and came out of the north. Coincidentally, at about this same time Harald Hardraada had completed his preparations for invasion and departed Norway with his fleet shortly thereafter. On his way south he was reinforced with ships and troops from his allies in the Shetlands and Orkneys and also by Tostig and the remnants of his small force, swelling his fleet to about 300 ships. After a couple of minor landings along the English coast, Harald sailed to Scarborough on the Northumbrian coast, which he probably arrived at on 15 September, burned the city, then sailed down to the Humber River, which he reached on 18 September.  Sailing up the Humber, then up the river Ouse, he went as far as possible by water, to the village of Riccall, about 12 miles from York, which was the capital of Northumbria and his objective.

Harald Marches on York
The fleet anchored at the village of Riccall on 19 September, where the Viking army disembarked, put on their armor, and commenced their march on York. News of the burning of Scarborough had reached York by this time. The Earl of Northumbria, Morcar, as well as his brother, Edwin, Earl of Mercia, were both present in York. They quickly gathered as many troops as they could. This was difficult because much of Northumbria's population was of Viking heritage and would not rally against them. Further, Edwin was too far away from Mercia and was unable to provide any more troops than those he currently had with him at York. Traditionally, English armies preferred to fight in the open rather than behind strong walls as their continental neighbors preferred. Therefore, on 20 September, Morcar and Edwin set out from York to intercept Harald and Tostig on open ground. The two armies met at Gate Fulford, about one mile south of York, and fought the first of the three battles that would decide the fate of Harold Godwinson, England, and the world.

It is estimated that Harald's army consisted of about 6,000 men and that about 1,000 of these were left behind to protect his all-important fleet at Riccall. Therefore, his fighting strength at Fulford Gate was probably about 5,000. The English army was smaller.

Morcar's Battle Disposition
Fortunately, Morcar reached Fulford Gate a few hours ahead of Harald and Tostig, and was able to deploy his small army to his liking. Without this prior positioning, the Vikings would have cut through the English like a hot knife through butter. The battleground was a swampy meadow situated between the Ouse and the track, or road, that the Vikings had been following from Riccall to York. Morcar formed a line whose right flank was anchored on the eastern bank of the Ouse, then stretched across the Fulford meadows to the track, and finally to a ditch on the other side of the track where the ground became so swampy that it was unsafe for troops to maneuver. This constituted Morcar's left flank. The line was several ranks deep, with the Housecarls in the forefront of the center, stretched out as far as possible, and flanked on their left and right by fyrdmen.

Harald's Battle Disposition
Harald lined up his army opposite Morcar's. He put his best men in the center of the line, where he was stationed, and on the left side of the line, where they stretched out to the eastern bank of the Ouse. This ground was considerably firmer than that on his right flank and would therefore enable him to use his best troops to the best advantage. He stationed his less experienced troops on the right flank, extending them to the point where the ground became too soggy to support a man's weight. He expected nothing more of his right flank than to hold their ground against the more experience English who were facing them. While the right held it's position, the center and left would crack the English line. Neither his left nor his right could be outflanked because the Ouse on the one side and the boggy ground on the other would prevent this.

The Battle
The battle began, it is certain, with each army advancing upon the other. Thousands of men were locked in mortal hand-to-hand combat with swords, axes and spears. Very quickly, Morcar's tough fyrdmen on the left began to push Harald's green troops back along the track. As the situation on his right began to look desperate, Harald quickly took the following action:  He ordered his left flank to spread out toward the center so that they could hold the left and as much of the center as possible and still maintain themselves against the English. Then he took the men who were under his personal command in the center, quickly wheeled them to the right and struck the advancing fyrdmen in their left flank. Being struck so suddenly and unexpectedly by a force that was superior both in numbers and experience, the fyrdmen were quickly destroyed. The English left, which had been doing so well, was now dissolved into small groups who fought desperately as they were driven back, not toward their old line, but  toward the ditch and the bogs. The morale of Harald's right was quickly revived and they joined in on the butchery. Harald's success on this end of the line proved to be decisive. Seeing what was happening there, Viking morale throughout the entire line was increased while that of the English was broken.  Shortly thereafter, the English right, over by the Ouse, was bent backward by the victorious Vikings and then the entire English line collapsed as the soldiers fled in disorder.

After the Battle
Following the battle, York fell to Harald and Tostig. Of course, the city came to terms without putting up any resistance. Among the terms forced upon the city administrators were that Harald would be given total and undisputed control of the city, that he could have anything he wanted from the city, and that the city and its inhabitants were to recognize Harald as their king and assist him in the forthcoming struggle against Harold Godwinson to wrest the kingdom of England from him. In return for accepting these conditions, the Vikings would not loot the city or otherwise damage it as was their usual custom.

There was one other condition, and it was to be the most important since it dictated the date and location for the second great battle of 1066. As a guarantee that they would fulfill their commitments; especially that of providing soldiery to assist him in the upcoming struggle with Harold Godwinson, Harald demanded 100 hostages. The battle of Fulford Gate and the ensuing terms of York's surrender occurred on Wednesday, 20 September 1066. The date and place for the delivery of the hostages was Sunday, 25 September, at Stamford Bridge.