"In the month of August, Harold, king of Norway, and Tostig, with a powerful fleet set sail over the wide sea, and, steering for England with a favourable aparctic, or north wind, landed in Yorkshire, which was the first object of their invasion. Meanwhile, Harold of England, having intelligence of the descent of the Norwegians, withdrew his ships and troops from Hastings and Pevensey, and the other seaports on the coast lying opposite to Neustria, which he had carefully guarded with a powerful armament during the whole of the year, and threw himself unexpectedly, with a strong force by hasty marches on his enemies from the north. A hard-fought battle ensued, in which there was great effusion of blood on both sides, vast numbers being slain with brutal rage. At last the furious attacks of the English secured them the victory, and the king of Norway as well as Tostig, with their whole army, were slain. The field of battle may be easily discovered by travellers, as great heaps of the bones of the slain lie there to this day, memorials of the prodigious numbers which fell on both sides."
From Orderic Vitalis, The Ecclesiastical History of England and Normandy,
Thomas Forrester, tr. vol. 2 (London: Bohn, 1853), pp. 275-288.
I am indebted to Kath Bonson for drawing this to my attention.