[1] According to Bede, a large number of monks from the monastery at Bangor on Dee who had come to witness the fight were killed on the orders of Æthelfrith before the battle.
[4] Historian Charles Plummer, best known as an editor of Bede, believed that the battle occurred around 615 or 616,[5] but near contemporary annals give a variety of dates.
He wrote that the monks: resorted...to pray at the...battle...King Æthelfrith being informed [of this]...said, "If then they cry to their God against us, in truth, though they do not bear arms, yet they fight against us, because they oppose us by their prayers."
He, therefore, commanded them to be attacked first ... About twelve hundred of those that came to pray are said to have been killed.This episode was also noted in the Annals of Ulster s.a. 612 (recte 613): Bellum Caire Legion ubi sancti occisi sunt (The battle of Caer Legion, in which holy men were slain)[9]Bede thought this was divine retribution for the Welsh bishops refusing to join Augustine of Canterbury in proselytizing the Saxons.
During the English Reformation scholars such as Matthew Parker frequently argued that Augustine himself had been complicit in the battle and the massacre, but this contention swiftly degenerated into a sectarian dispute.
[10] The argument relies on the 604 date for the battle found in the Anglo-Saxon Chronicle as well as the suggestion that a passage in Bede that specifically exculpates Augustine, which appears in the Latin but not in the early English translation of the text, was a later addition aimed at distancing the churchman from the violence he predicted.
Archaeological excavations at Heronbridge, just south of Chester, in 2004 uncovered post-Roman graves buried beneath a defensive earthwork over an old Roman settlement.
[11][12] The precise reasons for the battle are unknown but Geoffrey of Monmouth states that King Æthelfrith's political rival, Edwin of Deira, was living in exile in Gwynedd.
Although Geoffrey of Monmouth is often regarded as an unreliable source, there are some supporting references to Edwin in the writings of Reginald of Durham and the Welsh Triads.