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.
HistoryLayer draws the world as it was in any year from 123,000 BCE to
2026. Move the slider and the borders redraw for that year; the map
carries 23,890 events, 12,790 people, 837 wars and 13,183 cities, each
one readable in place. Signing in is optional and lets you keep what
you find.