Battle of Maserfield The Battle of Maserfield ( or Maserfeld , " marsh ( border ) field " ; Welsh : " Maes Cogwy " ) , was fought on 5 August 641 or 642 , between the Anglo - Saxon kings Oswald of Northumbria and Penda of Mercia , ending in Oswald ' s defeat , death , and dismemberment . The battle was also known as " Cogwy " to the Welsh , with their countrymen from Pengwern participating in the battle ( according to the " Canu Heledd " ) , probably as allies of the Mercians . Bede reports the commonly accepted date given above ; the Welsh " Annales Cambriae " is generally considered incorrect in giving the year of the battle as 644 . The site of the battle is traditionally identified with Oswestry ; arguments have been made for and against the accuracy of this identification . Background . Since the death of Oswald ' s uncle Edwin of Northumbria at Hatfield Chase in 633 , the Mercians under Penda had presented an obstacle to the power of Northumbria over the lands of Britain south of the Humber . Oswald had defeated Cadwallon ap Cadfan of Gwynedd , King of the Britons ( Penda ' s ally at Hatfield ) at Heavenfield in 634 , and subsequently re - established Northumbrian hegemony across much of Britain ; although it is thought that Penda recognized Oswald ' s authority in some form after Hatfield , he may nevertheless have been hostile to Northumbrian power or at least perceived by Oswald as a threat . Outbreak of war . The cause of the war that led to Maserfield is unknown . The historian Bede , writing in the next century , portrayed Oswald as a saintly figure in his " Historia ecclesiastica gentis Anglorum " ; his desire to portray Oswald in a positive light may have led him to omit mention of Oswald ' s aggressive warfare . He says only that Oswald died fighting for his country at Maserfield , giving the impression that the battle was part of a " just war " . The location of the battle is traditionally identified as Oswestry ( etymology : " Oswald ' s Tree " ) in Shropshire , which at that time is thought to have probably still been in the territory of Powys . If this location is correct , it would mean Oswald was in the territory of his enemies , which would suggest he was on the offensive . Penda ' s Welsh allies would have included Cynddylan ap Cyndrwyn of Powys ; the " Marwnad Cynddylan " says of him that " when the son of Pyd requested , how ready he was " . This may be a reference to Penda , the son of Pybba , meaning that Cynddylan was eager to fight in battle alongside him . Cadwaladr ap Cadwallon is also thought to have donated reinforcements to Penda from the Kingdom of Gwynedd . The battle . The outcome of the battle was defeat for the Northumbrians . Bede mentions the story that Oswald prayed for the souls of his soldiers when he saw that he was about to die . Oswald ' s body was cut into pieces , and his head and arms mounted on poles ; the parts were retrieved in the next year by his brother and successor Oswiu . Since Penda was a pagan and Oswald was Christian , the latter was subsequently venerated as a martyr and saint . Bede reports a number of miracles attributed to Oswald ' s bones and to the spot where he died . ( In the 12th century , Henry of Huntingdon wrote of the battle : " It is said the plain of Maserfeld was white with the bones of the Saints " . ) The " Historia Brittonum " accredits Penda ' s victory to " diabolical agency " , but the characterization of the battle as a clash between Christians and pagans may be oversimplified if there were Welsh , who were Christian , fighting on Penda ' s side . The 20th - century historian , D . P . Kirby , wrote that the battle left Penda as " without question the most powerful Mercian ruler so far to have emerged in the midlands . " According to the " Historia Brittonum " and the " Annales Cambriae " , Penda ' s brother Eowa , also said to have been a king of the Mercians , was killed in the battle along with Oswald . The possibility exists that he was subject to Oswald and fighting in the battle as his ally . It has been suggested that Eowa was the dominant king among the Mercians for a period prior to the battle , and it has also been suggested that he had ruled the northern Mercians while Penda ruled the southern Mercians . Since the " Historia Brittonum " says Penda ruled for only ten years ( Bede says 22 years : 633 – 655 ) , this may mean that it was dating Penda ' s reign from the time of his victory at Maserfield ; this would make sense if Eowa ' s death removed an important rival to Penda , enabling him to claim or consolidate authority over all the Mercians . Aftermath . Following the battle , Deira , in the southern part of Northumbria , chose a king of its own , Oswine , while Bernicia in the north ( which had been dominant , with Oswald , a member of the Bernician royal line , ruling both Bernicia and Deira prior to Maserfield ) was ruled by Oswald ' s brother Oswiu . Thus the battle led to the internal weakening and fracturing of the Northumbrian kingdom , a situation which lasted until after the battle of the Winwaed , despite Oswine ' s murder on the orders of Oswiu in 651 . According to Frank Stenton , Maserfield left Penda as " the most formidable king in England . " He maintained this position until his death against the Bernicians at the Battle of Winwaed in 655 ; at times in the years between the two battles , his power was sufficient that he could mount destructive raids into Bernicia itself , at one point besieging Bamburgh , prior to his final , doomed campaign .