The Eagle and the Raven by Pauline Gedge is a fantastic story about Iron-Age Britain just before, during, and after the Roman invasion under Claudius.
It mainly follows the fortunes - and misfortunes - of Caradoc (aka, Caractacus) who grows from being a wild youth happy to raid his neighbours, to being weighed down with the responsibility of leading an uprising against Roman occupation. We also follow Boudicca and other figures as the story develops.
It's a little slow to get started, but in the end it's a brilliantly-written and researched historical novel about the period, and really gives a great perspective of Roman occupation.
From an historical perspective, it is romanticised - the only legend missing from the story is that Caradoc's son, Lyn, become a Pope in Rome. However, Gedge does a great job of entwining many threads of myth together into a coherent story that conveys every sense of containing some truth.
The big flaw is that this book almost certainly influenced Braveheart, with its woaded warrior-chiefs rallying to the cry of "Freedom" - yet Gedge, for all her focus on this, misses the hypocrisy that these are the same people happy to keep slaves themselves.
Still, a great read and definitely one of the classics of Roman Historical Fiction.
Btw, the ebook is only £2.48 on Amazon UK - highly recommended over the much more expensive paperback.