The Book of Aneirin
Cardiff MS 2.81
Aneirin was a contemporary of Taliesin and Myrddin (Nennius mentions him under the name "Neirin" from the alternate spelling "Aneirin"). A poet in Urien's court, he was present at the battle of Cattraith, ca. 600 CE/AD in Catterick, Yorkshire, on which he wrote his epic poem Y Gododdin, about the defeat of the Britons against the Saxons. He is critical in some places of the rash behavior of the soldiers; in other places, he mentions knights familiar to us from Arthur's court: Peredur (from the Mabinogion, the Welsh name of Perceval), Owain (Chretien's Yvain), and Taliesin are all named in the poem. In fact, there is a reference to Arthur as a mighty warrior of the recent past.
Aneirin also is supposed to have written a number of gwarchanau (Welsh: lais, that is, short story-poems). Unfortunately, I have yet to find a full translation, as there have been none. (The Gwarchan Maelderew, supposedly written by Taliesin, which Douglas Monroe spuriously calls a book of Druidic magic, the Gorchan of Maeldrew--is a lament on a fallen warrior, not a book of spells.)
The manuscript we have here--Carddif MS 2.81--is usually dated to around 1255-1265. The poems it contains are thought to have been transmitted orally long before ever being transcribed, perhaps in the 9th or 10th century; this may account for the variant readings of some stanzas, which are found after the gwarchanau section.
Digital images of the manuscript can be found at Gathering the Jewels, a digital collection of the Cardiff Library, where the manuscript now resides.
Here is the manuscript, as I have reconstructed it through referencing the edition of The Four Ancient Books of Wales and the digital edtion mentioned above:
OTHER TRANSLATIONS:
Earliest Welsh Poetry by Joseph P. Clancy: This book contains a much more accurate (and I think more poetic) translation of the Gododdin. Also, I wrongly had posted his translation here without his permission. Please go and buy his books on the subject, they're very much worth tracking down.
The Celtic Heroic Age edited by John Carey. This version is an attempt at distinguishing between the "A" texts and "B" texts, which are muddled in the manuscript (hence the repetitions, and the "Second" Gododdin).