Oswi in 655 had a pitched battle with Penda at Winwæd in Yorkshire,[39] where the latter was defeated and slain. To celebrate this victory Oswi established twelve religious houses, six of which were in Deira (see Chapter IX.). Oswi died in 670, and his son Egfrid (or Ecgfrith) succeeded to the throne of Northumbria, which was now become a Christian and powerful kingdom. His short reign was marked by several military victories, the chief being his defeat of the King of Mercia, by which he gained the province of Lindiswards, or Lincolnshire; but in A.D. 685 Egfrid went across the Forth to repress a rising of the Picts, and in a great battle at Nectansmere in Yorkshire he and many of his nobles were slain, and with them fell the supremacy of ancient Northumbria. From this date to the establishment of the Heptarchy, Northumbria, though allowed to elect tributary rulers, was, except for a very short period, under the overlords of first Mercia and then Wessex. Green, in his "History of the English People,"[40] says that Northumbria was "the literary centre of the Christian world in Western Europe. The whole learning of the age seemed to be summed up in a Northumbrian scholar, Bæda--the Venerable Bede, later times styled him." The same writer adds: "From the death of Bæda the history of Northumbria is in fact only a wild story of lawlessness and bloodshed. King after king [tributary kings] was swept away by treason and revolt, the country fell into the hands of its turbulent nobles, the very fields lay waste, and the land was swept by famine and plague." In A.D. 827 Egbert found no difficulty, after subduing the rest of England, in coming to peaceful terms with the Northumbrian nobles, and reducing the whole country from the British Channel to the Forth into one kingdom. For some time before the close of the eighth century Northumbria had been subject to frequent attacks from the Northmen, or Danes, who mostly came from Denmark and Norway, who have been frequently described as sea-pirates, distinguished for courage and ferocity and a strong hatred to the Christian religion, they themselves being worshippers of Woden and the other pagan gods. Soon after the middle of the tenth century the Danes were no longer content to make marauding expeditions, but aspired to become owners of the soil, and in 867, after a great victory near the city of York, they practically took possession of Northumbria, and a few years later the whole of England north of the Thames was in their hands. The subsequent wars between Alfred the Great and the Danes belong more to the general history of England; it will suffice here to state that in 878 was concluded the treaty of peace known as "Alfred and Guthrum's Peace," whereby the Danish settlers were recognised and the land on the east and north of Watling Street given up to them, that is, nearly all the east side of England from the Thames to the Tweed, where they were to