David Morrissey also played a Roman soldier, named Bothos, in Centurion (2010). That film also dealt with Roman soldiers warring with the Celts in Britain.
Runes are featured heavily in the show and the opening credits. Runes did not appear until the second century AD, in Scandinavia. They did not appear in the Brittish isles until the Saxons and Frisians brought them in the fifth century.