Last Updated September 5, 2023.
Layamon was an English priest. He wrote his epic poem Brut in the early thirteenth century. If you want to know the contents of it, you should check out the excellent study guide available on this website. Here, we'll discuss the poem's major theme.
Brut is a history of Britain from the later Bronze Age to about the time of the rise of the Kingdom of Mercia. It's not what we'd recognize as history today, though. Half of it is a re-telling of the story of King Arthur, and a good portion of the rest is a recapitulation of myths about the settling of Britain by Trojans and the lineage of kings, some real and some not.
The poem is also something of a mish-mash. The material isn't original. Layamon copied much of his text from earlier ecclesiastical historians, and he simply rewrote stories that were current in his part of England during the time of Queen Eleanor. This makes its thematic structure haphazard. In fact, you can argue there isn't a theme, in the sense that Layamon was trying to impart a message. Rather, patterns emerge in his telling of the story, what Christopher Lloyd called "the structures of history" in his book by that name.
The most important of those structures is the vulnerability of Britain to invasion and its need for deliverance by an all-powerful savior. The Christian sub-text to this ought to be obvious, but even if you read Brut without that, you can see the pattern. Brutus the Trojan delivers Britain from prehistoric savagery. Arthur the war duke saves pagan Britain from post-Roman Dark Ages chaos. Oswiu preserves "true" Christianity from encroaching heresies. Layamon was telling a very Christian story without actually telling it. It was his way of claiming British history for the Church.
Perhaps the most important effect of Brut, which has nothing to do with its thematic structure, is its telling of the legend of King Arthur in Middle English instead of French or Latin. That popularized the story of Arthur in writing, where it had hitherto been a ballad, recited or sung. Writing it down in a local language made it accessible to later authors.