Nennius records that King Arthur fought twelve major battles. The texts of Nennius (AD 796), the Easter Annals, and the Anglo-Saxon Chronicle point to where these battles were geographically, but as in most things to do with King Arthur, there is room for debate as to where events really took place.
This list is believed not to be chronological. And the rhyming names in Nennius' original work, indicates that he probably took his list from a rhyming-poem. Nennius could well have taken names from a number of unrelated sources.
Some scholars believe that the Roman commander, Lucius Artorius Castus, and King Arthur point to them being the same person when you examine this battle record.
Nennius' list is
Battle 1. On the river Glein.
Battle 2, 3, 4 and 5. On the river Dubglas in the region of Linnuis.
Battle 6. On the river Bassas.
Battle 7. In the wood of Celidon/Cat Coit Celidon.
Battle 8. At castle Guinnion.
Battle 9. In the city of the Legion
Battle 10. On the river Tribruit
Battle 11. On Mount/Hill/Rock Agned or Breguoin
Battle 12. At Mount/Hill/Rock Badon.
Then there is the final battle
Camlann, King Arthur's final battle
Camlann, King Arthur had his final battle, in which he is mortally wounded, does not appear in Nennius
The Legend of King Arthur