In The Reign of Arthur, Christopher Gidlow says there is a discrepancy between Bede and the Welsh Annals (Annales Cambriae) in the date for the battle of Chester, with Bede dating it to 603 AD and Annales Cambriae at 613. He considers that the Annales Cambriae date is defective due to a scribal error, and says, "This is an easy mistake to explain away, caused by placing the event in the next numbered decade."
Quite true, such a mistake could easily be explained in that manner. But I don't think there is a discrepancy. My reading of Bede is that his account does not provide an exact date for the battle and that the information he does provide can accommodate the Annales Cambriae date without having to postulate a scribal error. Here's why.
613. The battle of Caer Legion. And there died Selyf son of Cynan. And Iago son of Beli slept.
Augustine urges the British bishops to cement Catholic unity and performs
a miracle in their presence. Retribution follows their refusal. [A.D. 603.]
[...] Augustine summoned the bishops and teachers of the nearest British province to a conference.... They asked that a second and fuller conference might be held.... The bishops would not recognise Augustine as their archbishop, saying among themselves that if he would not rise to greet them in the first instance, he would have even less regard for them once they submitted to his authority. Whereupon Augustine, that man of God, is said to have answered with a threat that was also a prophecy, that if they refused to preach to the English the way of life, they would eventually suffer at their hands the penalty of death.
[...] Some while after this, the powerful king Ethelfrid... raised a great army at the City of the Legions - which the English call Legacastir, but which the Britons more correctly named Carlegion - and made a great slaughter of the faithless Britons... It is said that of the monks who had come to pray about twelve hundred perished in this battle and only fifty escaped by flight....Thus, long after his death, was fulfilled Bishop Augustine's prophecy."
In the year of our lord 604, Augustine, Archbishop of Britain, consecrated two bishops, Mellitus and Justus.
Augustine was succeeded in the archbishopric by Laurence... on the 27th of February 610, Mellitus brought back [from Rome] letters from the Pope to God's beloved Archbishop Laurence.
Excavations by the Chester Archaeological Trust at Heronbridge, south of Chester, have discovered a 'battle cemetery' of approximately the right date.
"Part of a mass grave pit was exposed in which the bodies (all seemingly male like those excavated in the 1930s), aligned west-east, had been laid side by side in partially overlapping rows. Within a space measuring only three metres by two metres, there were at least fourteen individuals. Two skeletons were fully excavated and removed for analysis and radiocarbon dating. Both had clearly sustained fatal head injuries. The results of subsequent osteoarchaeological study (by Malin Holst of York Osteoarchaeology Ltd) confirmed them as males and showed that both had died as a result of several sword blows to the head. They were both well-built individuals and the elder, aged around forty, if not both, had been in battle before, suggesting that they may have been experienced soldiers.
Bone samples from the two skeletons removed from the mass grave, along with
two flax seeds from the fort ditch fill, were submitted to the Scottish Universities
Environmental Research Centre for Carbon 14 dating. The results for the former
were as follows:
Sample 1 = 95% probability within range AD 430-640, 59% probability within range AD 530-620.
Sample 2 =95% probability within range AD 530-660, 51% probability within range AD 595-645.
The date of the Battle of Chester - circa AD 613 - lies right in the middle of these date ranges and, in the absence of any other known substantial engagement in the area, the mass grave seems likely to be associated with that event."
It seems quite clear from Bede's account that the first conference happened in 603 and the second conference may have been later the same year, then there was a gap of unspecified length ("Some while after this") before the battle at Carlegion/Legacastir (modern Chester).
Bede says unequivocally that the battle took place after Augustine's death. He does not give the year of Augustine's death, except to say that it occurred in the reign of Aethelbert of Kent. However, a date range for Augustine's death can be deduced. He cannot have died before AD 604, as Bede says that Augustine consecrated bishops Mellitus and Justus in AD 604, and he must have died before 27 February 610 when the Pope sent letters to his successor Archbishop Laurence.
So the battle of Chester cannot have happened in AD 603, since Bede says it happened after Augustine's death and Augustine was still alive in 604. The Annales Cambriae date of 613 would be 9 years after the earliest date for Augustine's death (604) or 3 years after the latest date (610), which would be consistent with Bede's statement that it happened "long after" his death.
The radiocarbon dates for the skeletons from the Heronbridge excavation are consistent with this date. Though radiocarbon dating is not precise enough to differentiate between 603 and 613, it is consistent with the identification of 'Carlegion/Legacastir/Caer Legion' as Chester, rather than as Caerleon-on-Usk (whose name also means 'city of the legion').
As Christopher Gidlow argues in The Reign of Arthur, the dates in the Annales are unlikely to be exact to the year. Some of the other entries in the Annales around the same period can also be linked to events recorded by Bede, and these may give an idea of the likely range of error around the date. Here are all the events in the Annales that I can also find in Bede from 595 to 631 inclusive (18 years either side of the Battle of Chester):
So the dates in Annales Cambriae are 0-4 years earlier than the equivalent dates in Bede. Applying this to the date given in the Annales for the battle of Chester would suggest that the battle occurred some time in the period 613 to 617 AD, which is consistent with Bede's statement that it happened "long after" Augustine's death.
So on balance I would say this is the likeliest date range for the Battle of Chester, and I would need a good reason to place the battle outside this date range.
Full-text sources available online are linked in the text.
Bede, Ecclesiastical History of the English People. Translation by Leo Sherley-Price, Penguin Classics, ISBN 0-14-044565-X.
Gidlow, C. The Reign of Arthur: from history to legend. Sutton, 2004, ISBN