"Brunanburh" is actually a famous battle in ~937ad which resulted in the unification of the British Isles into what we now know as the "United Kingdom". To summarize quickly, it was an Anglo-Saxon victory, led by Æthelstan King of England, over the combined Norse-Celtic force which effectively forced all the kingdoms of the British Isles to consolidate into the positions they occupy today. A majority of the knowledge involving this battle are reflected in a poem which can be found freely on the internet\, as well as artifacts. It seems the exact location of the battle is still being determined even to this day.
The music itself is heavily influenced by atmospheric black metal, doom, funeral doom, as well as elements of melodic death metal. There are no vocals, nor is there a need for them. The emotions that play out through these tracks translate well I feel into moments during the conflict where you can imagine your own battle, tidings of peace between the raging storms, or a moment of triumph at a successful defense. The music helps express something different for everyone, and with no vocals there are no restrictions, save for one track with a raging battle for atmosphere.