This poem had been always known as the other Geoffrey of Monmouth book - the one that was written after his history and did not get incorporated into it and which as a result as never as popular as the other 2 books he wrote ("Prophecies of Merlin" and the History - with the earlier one incorporated in the latter). Written almost 15 years after the history was published, it may appear to be almost inconsequential and yet, if one reads it, they will find yet another kernel from the story of Arthur (so it could not have been so impossible to find). Plus it had been preserved and survived to our days (which does not necessarily mean it was important - that's now how those things worked).

Reviewing this book requires reviewing two separate things: the poem itself and the translation.

So let's start with the poem - written in 1,529 hexameter verses in ~1150, it had not always been attributed to Geoffrey of Monmouth. The current scholarship seems to be in agreement that it was his but that can change. So let's assume it's his - until we know more (that's part of the challenge and fun in medieval (and earlier) literature). It is very different from the history - it is didactic in places, with sidelines on the natural world (fishes from all things), cosmology and geography (survey of the islands in the neighborhood of the big island), it has dialogues which make one thinks of the Greek Philosophers, it has Taliesin (the Welsh bard who shows up to have a learned conversation and forgets to leave).

The History showed us Merlin as a boy and as a young man but then he fell off the story and we never saw him again - he was instrumental in making sure that Arthur existed but Arthur never met him. When we finally catch up with Merlin, he had been a kind and then a mad man, living in the woods for awhile (Wales has a lot of legends of wild men and that's what that particular part seems to be related to) and is now towards the end of his life. We get to hear what happened between when we last saw him and the current times but it is Taliesin who brings the bit of information that puts that in the proper timeline - the bard had been part of the party which followed Arthur and he was there when the king fell and was brought to the Isle of Apples/Avalon, where the local healer Morgen takes care of him. The name is not an invention - she exists in a lot of versions in Welsh mythology but that is the first written source to mention her - and with a bit of reinvention in the next decades and centuries, she will become Morgaine le Fey, the half sister of Arthur and a sorceress. But those times are yet to come - here she is just a healer. But another part of the legend is thus added to the growing account which will keep growing and mutating as times pass.

What makes that poem unusual is that the author does not claim to be translating or collating it - he is inventing new material. And that did not happen that often in these times (remember that even the History was supposedly a translation from a book he had... emphasis on supposedly).

The translation I read is the first (so it claims and I cannot find any others) English translation in verse. The translator's introduction reads like a shorter version of Wikipedia's articles on the sources (mostly Welsh of course), the author and the poem creation. There is one interesting part in there though - the one discussing the translation. He spends some time explaining why the iambic pentameter is the natural rhythm of an English-language epic poems and why hexameter worked so well for Latin and Greek (language structure, stresses and so on) and then goes onto a defense of the hexameter in English and his decision to use that for the translation. That decision is somewhat baffling. While hexameter can be made to work in English (Longfellow's "Evangeline" for example), Mark Walker is not Longfellow. It kinda works in some places and it really grates in others - and I wish he had gone for the iambic pentameter - I almost can see some places where the phrase wants to go that way and is forced into unnatural order and breaks so it goes where the translator wanted it to go. Here are the first three lines so you see what I mean (line breaks as per the translation; the Latin ones are not exactly like that - but that is hard to be done in a verse translation anyway):

"Merlin, his madness, the mischievous muse of the poet prophetic
I am preparing to sing; friend Robert peruse this my poem,
Glory of bishops, correct it now calmly with sensible pen-strokes,"

The same text, translated in 1925 by John Jay Parry(in prose) reads:

"I am preparing to sing the madness of the prophetic bard, and a humorous poem on Merlin; pray correct the song, Robert, glory of bishops, by restraining my pen."

(the full text is available here: https://www.sacred-texts.com/neu/eng/vm/vmeng.htm; the complete Latin text is here: https://www.sacred-texts.com/neu/eng/vm/vmlat.htm if someone wants it).

Add to this the decision to split the poem into parts and to add overviews/summaries for each part (complete with line numbers) before the poem itself and the edition was very annoying (once I stopped reading the summaries, it got better). I am not sure if the latter parts' translation grate less because I got used to the format or because they were less weird but it takes awhile to get used to the way the poem goes. And even then, some parts required almost a reshuffle to figure out what they mean (which goes back to my complaint about the decision to use hexameter.

PS: "Evangeline" can be read here: https://poets.org/poem/evangeline-tale-acadie. It does sound a bit weird at the start (the format is really weird in English) but it does not grate and it works. ( )