Celtic Britain (1979) traces the history of the Celts and Celtic culture from the arrival of the first scattered groups of settlers in Britain in the seventh century BC to the development of the kingdoms of medieval Scotland and Wales. Although a Celtic culture continued to flourish independently throughout the Roman and Saxon periods, influences from outside began to permeate Celtic society, particularly that of Christianity.
This book covers the Celtic presence in Britain from before the Romans through the flowering of the Arthurian legend. Lacking a written record, the early going leans heavily on archeology and surviving art. Many of the usual suspects begin to appear when the Romans do--Julius Caesar first (who Lloyd Robert Laing finds well supported by the evidence), Vercingetorix, Cunobelin (Shakespeare's Cymbeline) and Boudicaa, who evidently released a sacred hare as a ritual before campaigns. Laing sketches out a pre-Roman society that was fractious between Celtic tribes, not just fighting each other but arguing over whether or not the Romans were a good thing. It's clear that cross-Channel trade, travel, and even migration were robust in this period. The Celts were organized by tribe, rather than states, had fluid borders, and don't seem to have thought of the coast as one. Laing sides with those who believe in the historical Arthur, based on some mentions in the contemporaneous record at a time when the name was unusual, but finds the accretions (even the early ones) more entertaining than historical. Or perhaps political--Laing argues that some celebrated findings of his grave happened at opportune times for the monarch of the moment. There is abundant mining of the sources, of whom I find Gildas the most approachable (perhaps becauuse he wouldn't let the facts get in the way of a florid sentence). Here's a sample, referring to the arrival of immigrant (gasp!) Jutes. "The brood of curs burst from their lair of the barbarian lioness, in three Keels as they call warships in their tongue... At the orders of the accursed tyrant, they fixed their fearful claws upon the eastern part of the island, as though to defend it... Their dam, learning the success of the first contingent, sent over a larger draft of the satellite dogs... Thus were the barbairas introduced.... in the guies of soldiers taking great risks for their generous 'hosts' as the liars asserted. They demanded supplies which were granted, and for a long time shut the dog's mouth." Kristi Noem and Stephen Miller couldn't have said it better.