Question: 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?
{'answer': 'Battle of Chester', 'supporting_facts': [['Synod of Chester', 0], ['Synod of Chester', 1], ['Synod of Chester', 2], ['Battle of Chester', 1]]}