At the Battle of Beran Byrig or Beranburh the West Saxons are said to have defeated the Britons at Barbury Castle hillfort near Swindon in or around 556 AD according to the Anglo-Saxon Chronicle.
The Chronicle's entry for the year states:
556: Her Cynric 7 Ceawlin fuhton wiþ Brettas æt Beranbyrg
556: This year Cynric and Ceawlin fought with the Britons at Beran byrg.
The control of Barbury Castle and its surroundings is likely to have been strategically important for both sides, as it lies on the Ridgeway, a principal regional communication route.
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Text from the Wikipedia article “Battle of Beran Byrig”, available under CC BY-SA 4.0.