Lords of Battle
It's not a bad book, and raises some interesting points regarding similarities of military culture between British and Germanic kingdoms. Over all, it's not a bad introduction, if highly limited by the fact that the only good sources we have for the subject are heroic poems.
Heroic poems suck as military history. Seriously. Very difficult to interpret--rather like a historian trying to figure out the history of WWII based on Captain America comic books.
One conclusion Mr. Evans (err, Dr. Evans, this is a magnification of his PhD thesis) reached that I disagree vehemently with is his conclusion that the British used horses only as a means of operational mobility, invariably dismounting to fight. That this was true of the Germanic tribes I do not doubt, based on the lack of horse furniture in the grave goods, lack of description of mounted combat, etc.
But for the British, there is only offered a statement by RHC Davis that the native horse breeds of Britain averaged 8-10 hands. Again, I don't doubt this. The fact remains that the Notitia Dignitatum lists no less than five named cavalry cohorts in Britain at the end of the 4th century. Each of these would have had a book strength in the neighborhood of 500 troopers, plus a remount pool. I doubt that, given the difficulty in moving horses by ship, these horses were bred in Gaul or further afield. It is far more reasonable to assume that the Romans had stud farms with warhorse breeds to provide for their own troops. These horses would have be highly prized and not likely to have become extinct in the century after the Romans left. I have not read the Gododdin poem but I have it on order, and will judge for myself the statements made in this poem in regards to mounted warfare.
I am unconvinced of the statements by Dr. Evans definitely excluding those not full-time members of the 'comitatus' or professional warband from the practice of warfare. I am also unconvinced of the conclusion that the warband's ranks were refreshed only from the sons of the warriors, wandering mercenaries drawn by the chief's reputation, and fostered boys. It seems to me, given the apparently high casualty rates of battles and given the apparent lack of concern for any hereditary component to the warband's makeup (outside of the chief's immediate family) that any number of 'hangers-on' hoping to win a place in the chief's hall could have attached themselves to a warband. After all, not every Joe Snuffy that's going to show up with a spear and shield (huge economic investments? I think not) is going to have enough of a reputation to justify being taken on by the chief as a full-time professional fighter.
Just because the practice is not attested to in the poetry doesn't mean that it _didn't_ happen. I'm just leery enough about the reliability of epic poetry as a source of technical military details (especially when interpreted by some sillyvilian) that I am far less comfortable making definitive statements than Dr. Evans seems to be.
Then again, I doubt they hand out PhDs for saying, "There really isn't enough data to honestly tell much about subject X, Y, or Z. So let me inflate the chapters dealing with A, B, and C, about which the poets do go on and on about."