The odd couple of the Roman Legion
Meet Macro: veteran soldier, tough guy, rough around the edges, curse word using, seasoned campaigner. Recently promoted to Centurion.
Meet Cato: newbie, raw recruit, literature reading, former slave, with connections to high falutin people in Rome. Recently promoted (for dubious reasions) to Optio, Macro's second in command.
Macro takes Cato under his wing despite their differences, and as the Roman army goes from Germany to Britain, the two find themselves involved in various plots and schemes revolving around the newly installed emperor.
If you are looking for a good, light adventure story, this was a rollicking good read. If you really like it, there are more books in the series.