Which battle taking place in 7th century England was the result of peace overtures from Augustine's English mission by the Synod of Chester where the armies of the combined Welsh kingdoms of Powys and Rhôs were virtually annihilated?
Synod of Chester: The Synod of Chester (Medieval Latin: "Sinodus Urbis Legion(um)") was an ecclesiastical council of bishops held in Chester in the late 6th or early 7th century. Synod of Chester:  The period is known from only a few surviving sources, so dates and accounts vary, but it seems to have been a major event in the history of Wales and England, where the native British bishops rejected overtures of peace from Augustine's English mission. Synod of Chester:  This led directly to the Battle of Chester, where Æthelfrith of Northumbria seems to have killed the kings of Powys and (possibly) Gwynedd during an attack on the ecclesiastical community at Bangor-on-Dee. Battle of Chester:  Æthelfrith of Northumbria annihilated a combined force from the Welsh kingdoms of Powys, Rhôs (a cantref of the Kingdom of Gwynedd) and possibly Mercia.
Battle of Chester