Beginning in 117 AD, the narrative opens with a Roman soldier fleeing across a snowy landscape, saying: "My name is Quintus Dias. I am a soldier of Rome, and this is neither the beginning, nor the end of my story."
The Romans have been unable to fully conquer Britain, meeting the fiercest resistance in the north, and the Picts of Alba are engaging in a guerrilla campaign against the Roman forts along the Glenblocker line and the Gask Ridge at the southern border of the Scottish Highlands. At the Roman outpost of Pinnata Castra, Pictish warriors led by Vortix and Aeron force surprise and kill the entire garrison, taking only one survivor for questioning, the second-in-command, Centurion Quintus Dias, because he can speak the Pictish tongue. Dias is brought before the Pictish king Gorlacon, who has united the northern tribes. Dias is brutally interrogated, but two weeks later escapes on foot.
However, a messenger dispatched by the fort's commander has reached Gnaeus Julius Agricola, the Roman governor of Britannia, who wants to obtain favour with the Roman Senate, hoping to secure a transfer back to the comforts of Rome. He dispatches the Ninth Legion, under General Titus Flavius Virilus, to eradicate the Pictish threat and provides him with a female Celtic Brigantian scout called Etain. As the legion marches north it encounters Dias and rescues him from his pursuers.
Etain betrays the legion to Gorlacon, leading them into an ambush where they are annihilated. The general is captured. Dias is one of the few survivors, along with the legionaries Bothos, Thax, Brick, Macros and Leonidas, and Tarak, a cook. They set out to rescue general Virilus and, after a few days' travel, they find him at Gorlacon's village and sneak in at nightfall. However, they are unable to break his chains and he orders them to leave him and get back to Roman territory. During the attack, Thax, taking shelter in Gorlacon's hut, suffocates the king's young son to prevent him crying out.
The next morning, Gorlacon burns his son's body on a funeral pyre and forces General Virilus to fight Etain in single combat. She kills him and Gorlacon then sends her after the fleeing legionaries at the head of a small group of mounted warriors, including Vortix and Aeron, to seek revenge for his son's death.
The seven Romans plan to travel north (away from Roman territory) to throw the Picts off their trail, then head west, and then back south. After several days' pursuit, the Picts catch up with the fugitives, who jump off a cliff into a river to escape them, although Tarak is killed before he can jump. Macros and Thax become separated from the others. Dias and his group camp for the night, while their trackers set up camp across the river. Dias and Brick launch a night raid on the enemy camp, killing two men and severely wounding a third, from whom they discover that they are being pursued because of the death of Gorlacon's son, which Thax kept secret. However, Etain has launched her own attack on the Romans' campsite. Dias and Brick return to their camp to discover Leonidas dead and Bothos wounded.
Macros and Thax are now running from a wolf pack. Thax pretends to fall, with the wolves in close pursuit, and cries out to his comrade for help. Macros returns to help him and Thax hamstrings him to prevent him from standing, allowing Thax to escape while the wolves attack and devour Macros. Dias, Bothos and Brick find a hut in the forest belonging to Arianne, a Pictish exile accused of witchcraft who has learned Latin from the soldiers at a nearby Roman frontier outpost. She shelters them, providing food, and medical attention for Bothos. When Etain and her warriors arrive the following day, Arianne confronts her while the Romans hide in her grain store under the floorboards. The next morning they leave Arianne, who provides them with enough food to travel to the outpost.
They find the outpost abandoned, with an order pinned to a post saying that the Roman troops have retreated south, by the orders of the Emperor Hadrian. Seeing Etain and her warriors approaching and fed up with running, they set up a defensive position inside the fort. Brick is killed, but the three Romans kill Vortix, Aeron, and the rest of the Picts, with Dias ending the fight by killing Etain.
Taking the Picts' horses, Dias and Bothos continue southwards and en route are reunited with Thax. Upon reaching Hadrian's Wall, which is now under construction, Thax, afraid that he will report his actions, threatens Dias and they fight, with Dias killing Thax. Bothos, joyfully riding towards the Romans, is mistaken for a Pict because of his clothes and is shot by an archer. Dias reports to Agricola, who is concerned that news of the legion's annihilation might cause other tribes to rise up against them. He is also fearful of his record being tainted by a military failure, and decides that the Ninth Legion's fate should remain a mystery and that Dias must be killed. Dias, however, manages to foil the attempt on his life by Agricola's daughter, although he is badly wounded in the thigh during the fracas. He escapes from the camp and returns to Arianne in the forest. As the weakened Dias lies in her arms by the stream, he and Arianne kiss. The film ends with Quintus Dias adjusting the narrative of the film's opening line:
"My name is Quintus Dias. I am a fugitive of Rome, and this is neither the beginning, nor the end of my story."Michael Fassbender as Quintus Dias, a centurion. His father was Scipio Dias, a renowned and later freed gladiator. Formerly the second-in-command at the Inchtuthil garrison, Quintus is the only survivor of the fort and the only Roman to escape King Gorlacon. Quintus joins the Ninth Legion's march into Caledonia and is later betrayed by governor Agricola.
Olga Kurylenko as Etain, a warrior, scout, hunter and tracker from the Brigantes tribe. After seeing her family raped and murdered by the Romans, Etain was raped herself and had her tongue cut out. She fled north and was taken in by the Picts, who trained her and sent her back to the Romans as a spy. Marshall said of the character, "Etain is kind of revenge incarnate. Her family were butchered by the Romans, she had her tongue cut out by the Romans, she's had a hell of a time and she's out for Roman blood... She's quite furious because one sense is not there – she can’t speak – all the others are more developed. She sees very well and hears very well: she is an animal!"
Dominic West as Titus Flavius Virilus, the general (legate) of the Ninth Legion. Virilus is a tough veteran, far more comfortable with the ordinary soldiers, who would follow him anywhere, than with his fellow patricians.
Liam Cunningham as Brick (Ubriculius), a veteran legionary of the Ninth Legion. He is on his last tour before settling down on a farm in Tuscany.
David Morrissey as Bothos, a veteran legionary in Septus's century of the Ninth Legion. He joined the army as an orphan on the streets of Rome.
JJ Feild as Thax, a self-serving legionary in Septus's century of the Ninth Legion.
Noel Clarke as Macros, a legionary of the second cohort of the Ninth Legion. Originally from Numidia, he was a noted marathon runner in Greece before joining the army.
Riz Ahmed as Tarak, a cook with the Ninth Legion, originally from the Hindu Kush.
Dimitri Leonidas as Leonidas, a half-Greek legionary scout of the Ninth Legion.
Ulrich Thomsen as Gorlacon, the leader of the Picts.
Imogen Poots as Arianne, a young Pictish woman exiled for witchcraft by Gorlacon.
Dave Legeno as Vortix, an axe-wielding Pictish warrior.
Axelle Carolyn as Aeron, a Pictish archer.
Paul Freeman as Gnaeus Julius Agricola, Roman governor of Britannia. This is an anachronism; the historical Julius Agricola was actually governor some 20–30 years before the events depicted in the film, and was already dead by the time Hadrian's Wall began construction. The governor at the time of the Pictish war, the disappearance of the Ninth Legion and the beginning of the construction of Hadrian's Wall in 119 AD was actually Quintus Pompeius Falco.
Rachael Stirling as Druzilla, Governor Agricola's daughter.
Michael Carter as Antoninus, one of Agricola's generals.
Tom Mannion as Tesio, one of Agricola's generals.
Peter Guinness as Cassius, one of Agricola's generals.
Lee Ross as Septus, a veteran centurion of the Ninth Legion and an old friend of General Virilus.
Jake Maskall as Argos, an officer of the Ninth Legion, one of General Virilus's aides.
Eoin Macken as Achivir, a Pictish warrior.
Neil Marshall as Archer on Hadrian's Wall, an uncredited cameo as the watchman who mistakes Bothos for a Pict.
Centurion was written originally by director Neil Marshall under the working title Ninth Legion. The Ninth Legion, according to one legend, marched into Scotland from York with over 3,000 men and disappeared. In recent years, historians have disputed the fate of the legion; some believe they were disbanded, while others believe they were massacred in Germania or in the East fighting the Persians during the early years of the second century. Marshall said of his take of the story, "It's not meant to be historically perfect. I'm picking up on a legend and exploring it... it's an action thriller." The tide of academic opinion seems to be returning to the view that the Legion was probably wiped out in Britain. In a recent book, Dr Miles Russell of Bournemouth University observes that there is strong evidence for a catastrophic British war resulting in the annihilation of the legion early in the reign of Hadrian.
Filming began towards the end of February 2009. Filming locations included the Scottish locations Badenoch, Strathspey, and Glenfeshie Estate in the Cairngorms. Filming also took place at Ealing Studios in London and in Surrey locations, such as Alice Holt Forest and Hurtwood Forest in the Surrey Hills. Historical re-enactment groups were enlisted to play Picts and Roman soldiers in the practical filming at Badenoch and Strathspey. Filming was completed in March, after seven weeks. Production design was by Simon Bowles, with art direction by Jason Knox-Johnston. The sets were built by DRS Construction.
The film was screened on 18 March 2010 at the South by Southwest Film Festival as the "Super Secret TBD" film. It was also the opening night premiere for the inaugural ActionFest film festival. The film was released on 30 July 2010 as video on demand on the Xbox Live Marketplace and Amazon.com.
The film received mixed to positive reviews, and currently has a 59% ranking on Rotten Tomatoes and 62/100 on Metacritic. The Birmingham Post gave the film two stars out of five saying "this hideously violent, formula one chase movie lacks the novelty of Mel Gibson's Apocalypto". Empire Magazine gave the film three stars out of five stating that the film "could have done with a lot more character-meat on those bones." Film4 gave the film two stars out of five stating "It's just a shame none of this stuff was thought through a little more carefully, because there's a talented cast here who have been hung out to dry." The Guardian gave the film two stars out of five stating that "this is exercise-bike cinema: energetic, relentless and tipping towards monotony".