Update 02/10/2022 - I read through another edition of De excidio Britanniae today, mainly to see whether there were any differences in translation with the version I read in 2015 - review below. The version I have just read was a 19th century one edited by a Hugh Williams, and it includes the Latin text as well as the English translation. The Williams version also includes a range of other writings by or attributed to Gildas, of a purely religious nature.
The translation was similar to the version I read in 2015, but there was one significant difference in interpretation. Gildas refers at one point to a rebellion by the Britons against the Romans, which came from "the treacherous lioness", leaena dolosa are the words he uses. The use of the word "lioness" has commonly been taken as a reference to Queen Boudicca and her famous revolt of 62AD, - see my original review - but Dr Wiliams believed that the word referred to Britain as a whole. He bolsters his case by pointing out that on several other occasions Gildas uses the term "lioness" to describe a country. The arrival of the Saxons is described with the words Tum erumpens grex catulorum de cubili leaenae barbarae - "A brood of cubs burst forth from the lair of the barbarian lioness". Later when denouncing a local British king of Devon (Gildas does a great deal of denouncing) he describes said king as leaenae Damnoniae tyrannicus catulus "tyrannical cub of the Devon lioness".
The reader can take their choice as to which they prefer. I suppose if nothing else the example shows that interpreting ancient texts can be a tricky business.
Original Review
About 30 years ago I read a book called "Celtic Britain" in which the author quoted from this work. At the time I never thought I'd read the original (even in translation) but in the intervening period the Internet has come to be and made these texts much more accessible.
Gildas was a Romano-British monk, thought to have lived in the early to mid 6th century, and just about the only contemporary source for the early Dark Ages in Britain. The English language title of this is normally given as "On The Ruin of Britain", and how it would have pained Gildas to learn that his book had been translated into the language descended from that spoken by the hated Saxons!
I was actually a bit surprised at how short this text is. It can be read in about half an hour, and to say that Gildas is critical of his fellow Britons is a bit of an understatement. The book is basically an extended rant against his own countrymen for their supposed cowardice and sinfulness. For Gildas, the Romans were definitely the good guys, constantly rescuing the wretched Britons from their enemies. Queen Boadicea is described as "that deceitful lioness" (and it is clear that the term "lioness" is not meant as a compliment).
Much of the history is pretty confused, but Gildas appears to have some knowledge of Northern Britain, since he refers to "two foreign nations... the Scots from the northwest, and the Picts from the north," which accurately describes the homelands of those peoples. Interestingly they are described as "differing from one another in manners".
"On The Ruin of Britain" sounds as if it could be the title of a UKIP election leaflet, and indeed the last part of the book is a sort of warning of the supposed dangers of immigration, with the twist that here it is the English who are the immigrants. According to Gildas it was King Vortigern who sealed the country's fate by inviting in "the fierce and impious Saxons, a race hateful to God and men, to repel the invasions of the northern nations". The Saxons then spread across the country "to the western ocean" until the Britons managed to gather strength under a new leader, Ambrosius Aurelianus, who "of all the Roman nation" was "by chance left alive." Gildas relates that with this new leader the Britons won many victories, especially Mons Badonicus, "the last almost, but not the least slaughter of our cruel foes."
The fact that the only contemporary source from this period makes no mention of King Arthur has been well debated by historians, and some have concluded that Ambrosius Aurelianus may have been the inspiration for Arthur. That though, is a whole different subject.