Harrison is referring to the battle of Chester, fought between 613 and 616, at which according to Bede the monks of Bangor who had come to pray for a British victory were attacked by the forces of Aethelfrith, king of Northumbria, and 1200 (not 2100) of them killed. It was not fought `in the quarell of Augustine the monke', who had died in 604, but Augustine was said to have threatened the British bishops and monks with divine vengeance if they did not adopt Roman practice and accept him as archbishop - Historia Ecclesiastica Book II c.2.