Battle of Winwaed
The Battle of the Winwaed was fought on November 15, 655 between King Penda of Mercia and Oswiu of Northumbria, ending in the Mercians' defeat and Penda's death.Although said to be the most important battle between the northern and southern divisions of the Anglo-Saxons in early Britain, few details are available. For instance, the two armies met on the banks of a river named the Winwaed, but this river has never been identified. (Most likely it was a tributary of the Humber.)
The roots of the battle lay in Penda's success in dominating England in the 630s and 640s. He had defeated Edwin of Northumbria at Hatfield Chase in 633 and Oswald of Bernicia at the Battle of Maserfield in 642. Mercian warriors regularly raided into Northumbria, as far north as Bamburgh, and the Northumbrian sub-kingdom of Deira supported them against Oswiu beginning around 653.
Oswiu presumably resisted Penda's demands, and Penda, after gathering allies from East Anglia and Wales, marched with a force "thirty legions strong". It is almost certain that the Northumbrians were considerably outnumbered by the Mercians and their allies, and Penda seems to have rejected Oswiu's offers of treasure in exchange for peace. According to Bede, before the battle Oswiu prayed to God and promised to make his daughter a nun and grant twelve estates for the construction of monasteries if he was victorious.
As the battle was joined, two of Penda's allies, Cadfael ap Cynfeddw of Gwynedd (thereafter remembered as "Battle-Shirker") and Aethelwald of Deira, deserted him. Penda was soundly defeated, and both he and the East Anglian king Aethelhere were killed.
After the battle, Oswiu took part of Mercia for himself, leaving the rest to Penda's son Peada.