Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
AT this time, King Oswy was exposed to the cruel and intolerable invasions of Penda, king of the Mercians, whom we have so often mentioned, and who had slain his brother; at length, compelled by his necessity, he promised to give him countless gifts and royal marks of honour greater than can be believed, to purchase peace; provided that he would return home, and cease to waste and utterly destroy the provinces of his kingdom. The pagan king refused to grant his request, for he had resolved to blot out and extirpate all his nation, from the highest to the lowest; whereupon King Oswy had recourse to the protection of the Divine pity for deliverance from his barbarous and pitiless foe, and binding himself by a vow, said, "If the pagan will not accept our gifts, let us offer them to Him that will, the Lord our God." He then vowed, that if he should win the victory, he would dedicate his daughter to the Lord in holy virginity, and give twelve pieces of land whereon to build monasteries. After this he gave battle with a very small army: indeed, it is reported that the pagans had thirty times the number of men; for they had thirty legions, drawn up under most noted commanders. King Oswy and his son Alchfrid met them with a very small army, as has been said, but trusting in Christ as their Leader; his other son, Egfrid was then kept as a hostage at the court of Queen Cynwise,in the province of the Mercians. King Oswald’s son Oidilwald, who ought to have supported them, was on the enemy’s side, and led them on to fight against his country and his uncle; though, during the battle, he withdrew, and awaited the event in a place of safety. The engagement began, the pagans were put to flight or killed, the thirty royal commanders, who had come to Penda’s assistance, were almost all of them slain; among whom was Ethelhere, brother and successor to Anna, king of the East Angles. He had been the occasion of the war, and was now killed, having lost his army and auxiliaries. The battle was fought near the river Winwaed, which then, owing to the great rains, was in flood, and had overflowed its banks, so that many more were drowned in the flight than destroyed in battle by thc sword.
Then King Oswy, according to the vow he had made to the Lord, returned thanks to God for the victory granted him, and gave his daughter Elfled, who was scarce a year old, to be consecrated to Him in perpetual virginity; bestowing also twelve small estates of land, wherein the practice of earthly warfare should cease, and place and means should be afforded to devout and zealous monks to wage spiritual warfare, and pray for the eternal peace of his nation. Of these estates six were in the province of the Deiri, and the other six in that of the Bernicians. Each of the estates contained ten families, that is, a hundred and twenty in all. The aforesaid daughter of King Oswy, who was to be dedicated to God, entered the monastery called Heruteu,or, "The Island of the Hart," at that time ruled by the Abbess Hilda, who, two years after, having acquired an estate of ten families, at the place called Streanaeshalch,built a monastery there, in which the aforesaid king’s daughter was first trained in the monastic life and afterwards became abbess; till, at the age of fifty-nine, the blessed virgin departed to be united to her Heavenly Bridegroom. In this monastery, she and her father, Oswy, her mother, Eanfled, her mother’s father, Edwin, and many other noble persons, are buried in the church of the holy Apostle Peter. King Oswy concluded this war in the district of Loidis, in the thirteenth year of his reign, on the 15th of November, to the great benefit of both nations; for he delivered his own people from the hostile depredations of the pagans, and, having made an end of their heathen chief, converted the Mercians and the adjacent provinces to the grace of the Christian faith.
Diuma was made the first bishop of the Mercians, as also of Lindsey and the Midland Angles, as has been said above,and he died and was buried among the Midland Angles. The second was Ceollach, who, giving up his episcopal office before his death, returned into Scotland. Both these bishops belonged to the nation of the Scots. The third was Trumhere, an Englishman, but educated and ordained by the Scots. He was abbot of the monastery that is called Ingetlingum,and is the place where King Oswin was killed, as has been said above; for Queen Eanfled, his kinswoman, in expiation of his unjust death, begged of King Oswy that he would give Trumhere, the aforesaid servant of God, a place there to build a monastery, because he also was kinsman to the slaughtered king; in which monastery continual prayers should be offered up for the eternal welfare of the kings, both of him that was murdered, and of him that commanded the murder. The same King Oswy governed the Mercians, as also the people of the other southern provinces, three years after he had slain King Penda; and he likewise subdued the greater part of the Picts to the dominion of the English.
At this time he gave to the above-mentioned Peada, son to King Penda, because he was his kinsman, the kingdom of the Southern Mercians,consisting, as is said, of 5,000 families, divided by the river Trent from the Northern Mercians, whose land contains 7,000 families; but Peada was foully slain in the following spring, by the treachery, as is said, of his wife,during the very time of the Easter festival. Three years after the death of King Penda, the Mercian chiefs, Immin, and Eafa, and Eadbert, rebelled against King Oswy, setting up for their king, Wulfhere,son to the said Penda, a youth whom they had kept concealed; and expelling the ealdormen of the foreign king, they bravely recovered at once their liberty and their lands; and being thus free, together with their king, they rejoiced to serve Christ the true King, for the sake of an everlasting kingdom in heaven. This king governed the Mercians seventeen years, and had for his first bishop Trumhere, above spoken of; the second was Jaruman; the third Ceadda; the fourth Wynfrid. All these, succeeding each other in order under King Wulfhere, discharged episcopal duties to the Mercian nation.