Centurion (2010)

Directed by Neil Marshall, Centurion (2010) is a historical action thriller set during the Roman Empire’s campaign in northern Britain. Starring Michael Fassbender and Olga Kurylenko, the film follows a group of Roman soldiers struggling to survive after being ambushed behind enemy lines by Pict warriors. Combining military combat with survival-driven pursuit across hostile wilderness, the story focuses on warfare, revenge and endurance in ancient Britain.

Från IMDB:
A splinter group of Roman soldiers fight for their lives behind enemy lines after their legion is devastated in a guerrilla attack.