text: The prior bretwalda, Ceawlin, is recorded by the Anglo-Saxon Chronicle as having fought Æthelberht in 568 at a place called "Wibbandun" ("Wibba's Mount") whose location has not been identified. The entry states that Æthelberht lost the battle and was driven back to Kent. Comparison of the entries concerning the West Saxons in this section of the Chronicle with the West Saxon Genealogical Regnal List shows that their dating is unreliable: Ceawlin's reign is more likely to have been approximately 581–588, rather 560–592 as claimed in the Chronicle.
  At some point Ceawlin lost his overlordship, perhaps after a battle at Fethan leag, thought to have been in Oxfordshire, which the Chronicle dates to 584, some eight years before he was deposed in 592 (again using the Chronicle's unreliable dating). Æthelberht certainly was a dominant ruler by 601, when Gregory the Great wrote to him: Gregory urges Æthelberht to spread Christianity among those kings and peoples subject to him, implying some level of overlordship. If the battle of Wibbandun was fought c. 590, as has been suggested, then Æthelberht must have gained his position as overlord at some time in the 590s. This dating for Wibbandun is slightly inconsistent with the proposed dates of 581–588 for Ceawlin's reign, but those dates are not thought to be precise, merely the most plausible given the available data.