Their first target was the territories of the Earls Morcar and Edwin, two men whose local forces had turned back Tostig when he attempted his solo return to England not long before. Harald stopped at the Orkneys to gather allies and supplies, then landed in England and joined up with Tostig, who had some ships and soldiers with him. Their first target was York.
Edwin and Morcar had brought their forces to bear, but they were in a difficult position. The River Ouse was on their right, and on their left was a swampy area called the Fordland. This also left Harald with the high ground.
Estimates are that the Norwegian army numbered about 6000 to the English 5000. There were heavy casualties on both sides.
The English attacked first; Harald's forces had not all arrived, and in fact his weaker battalions were first at the front. The English looked successful at first, but then the stronger and fresher battalions arrived. Although Harald was outnumbered, he was able to push the English back. More and more Norwegian troops were arriving g, adding fresh fighters to the battle against the tiring English. The English were finally defeated, although Edwin and Morcar survived.
York surrendered to the invaders, on the condition that the Norwegians would not force their way into the city.Tostig probably arranged this, since he wished to take over the city himself and would not want it looted. Hostages from York were arranged, and the Norwegian army went seven miles east to Stamford Bridge where they could make camp and rest.
King Harold in the south then decided to pull his armies from the coast and march them north as fast as possible to deal with the threat of his brother Tostig. Within a week of the Battle of Fulford—a remarkably short span of time—he surprised the Norwegians at Stamford Bridge. That story is for next time.