Thirteen years after Maserfield, he suffered a crushing defeat by Oswald's successor and brother Oswiu and was killed at the Battle of the Winwaed in the course of a final campaign against the Bernicians.

The source for Penda's life which can most securely be called the earliest, and which is the most detailed, is Bede's Ecclesiastical History of the English People (completed c. 731; chapters II.20, III.7, III.16–18, III.21, III.24).

[16]) Besides Eowa, the pedigrees also give Penda a brother named Coenwalh from whom two later kings were said to descend, although this may instead represent his brother-in-law Cenwalh of Wessex.

[24] The noted 20th-century historian Frank Stenton was of the opinion that the language used by Bede "leaves no doubt that ... Penda, though descended from the royal family of the Mercians, only became their king after Edwin's defeat".

[21] Given the apparent problems with the dates given by the Chronicle and the Historia, Bede's account of the length of Penda's reign is generally considered the most plausible by historians.

Cadwallon apparently was initially unsuccessful, but he joined with Penda, who is thought to have been the lesser partner in their alliance,[32] to defeat the Northumbrians in October 633[2] at the Battle of Hatfield Chase.

Penda's successful participation in the battle of Hatfield Chase would have elevated his status among the Mercians and so enabled him to become king, and he might have withdrawn from the war before Heavenfield to secure or consolidate his position in Mercia.

[35] Since the potential existed for Eadfrith to be put to use in Mercia's favour in Northumbrian power struggles while he was alive, it would not have been to Penda's advantage to have him killed.

[38] That Penda ruled the southern part is a possibility suggested by his early involvement in the area of the Hwicce, to the south of Mercia,[42] as well as by the fact that, after Penda's death, his son Peada was allowed to rule southern Mercia while the northern part was placed under direct Northumbrian control.

[43] Another possibility was suggested by Brooks: Penda might have lost power at some point after Heavenfield, and Eowa may have actually been ruling the Mercians for at least some of the period as a subject ally or puppet of Oswald.

If Eowa was dominant among the Mercians during the period leading up to the battle, then his death could have marked what the author of the Historia Brittonum regarded as the beginning of Penda's ten-year reign.

[56] Who governed the West Saxons during the years of Cenwealh's exile is unknown; Kirby considered it reasonable to conclude that whoever ruled was subject to Penda.

At one point before the death of Bishop Aidan (31 August 651), Bede says that Penda "cruelly ravaged the country of the Northumbrians far and near" and besieged the royal Bernician stronghold of Bamburgh.

When the Mercians were unable to capture it—"not being able to enter it by force, or by a long siege"—Bede reports that they attempted to set the city ablaze, but that it was saved by a sacred wind supposedly sent in response to a plea from the saintly Aidan: "Behold, Lord, how great mischief Penda does!"

Bede wrote that Penda tolerated the preaching of Christianity in Mercia itself, despite his own beliefs: Nor did King Penda obstruct the preaching of the word among his people, the Mercians, if any were willing to hear it; but, on the contrary, he hated and despised those whom he perceived not to perform the works of faith, when they had once received the faith, saying, "They were contemptible and wretched who did not obey their God, in whom they believed."

[64] Middle Anglia as a political entity may have been created by Penda as an expression of Mercian power in the area following his victories over the East Angles.

Previously there seem to have been a number of small peoples inhabiting the region, and Penda's establishment of Peada as a subking there may have marked their initial union under one ruler.

The districts corresponding to Shropshire and Herefordshire, along Mercia's western frontier near Wales, probably also fell under Mercian domination at this time.

[65] In 655,[1] Penda invaded Bernicia with a large army, reported to have been 30 warbands, with 30 royal or noble commanders (duces regii, as Bede called them), including rulers such as Cadafael ap Cynfeddw of Gwynedd and Aethelhere of East Anglia.

On the other hand, it has been argued that an issue of punctuation in later manuscripts confused Bede's meaning on this point and that he in fact meant to refer to Penda as being responsible for the war.

It would seem that Penda's army then moved back south, perhaps returning home,[71] but a great battle was fought near the river Winwaed in the region of Loidis, thought to be somewhere in the area around modern day Leeds, on a date given by Bede as 15 November.

The Cock Beck meanders its way through Pendas Fields, close to an ancient well known as Pen Well on the outskirts of Leeds, before eventually joining the River Wharfe.

According to the Historia Brittonum, Cadafael of Gwynedd, "rising up in the night, escaped together with his army" (thus earning him the name Cadomedd, or "battle-shirker"),[25] and Bede says that at the time of the battle, Aethelwald of Deira withdrew and "awaited the outcome from a place of safety".

[71] At a time when the Winwaed was swollen with heavy rains, the Mercians were badly defeated and Penda was killed, along with the East Anglian king Aethelhere.

Bede says that Penda's "thirty commanders, and those who had come to his assistance were put to flight, and almost all of them slain," and that more drowned while fleeing than were killed in the actual battle.

[73] With the defeat at the Winwaed, Oswiu came to briefly dominate Mercia, permitting Penda's son Peada to rule its southern portion.

While our understanding of Penda's reign is quite unclear, and even the very notable and decisive battles he fought are surrounded by historical confusion, for the first time a general outline of important events regarding the Mercians becomes realistically possible.

According to Stenton, had it not been for Penda's resistance, "a loosely compacted kingdom of England under Northumbrian rule would probably have been established by the middle of the seventh century.

"[76] In summarising Penda, he wrote the following: He was himself a great fighting king of the kind most honoured in Germanic saga; the lord of many princes, and the leader of a vast retinue attracted to his service by his success and generosity.

Many stories must have been told about his dealings with other kings, but none of them have survived; his wars can only be described from the standpoint of his enemies ...[77]Penda's wife is identified as Queen Cynewise or Kyneswitha.