The film is narrated by Ambrosinus, native to Britain, who knows of a legend concerning the sword of Julius Caesar, which was hidden away from evil men. It begins shortly before the coronation of Romulus Augustulus as Emperor in AD 475.

Having travelled through much of the known world in search of Caesar's sword, Ambrosinus has then become the tutor to the young Romulus. A Druid and part of a secret brotherhood protecting the sword, he at times gives the impression he is a magician, but his "magic" is usually revealed to be simple trickery. One of the running concepts of the movie surrounds the question of whether or not Ambrosinus has any actual magical abilities or simply an illusionist. Romulus's father Orestes rules Rome but is not Emperor himself.

On the day before the coronation, Odoacer, commander of the barbarian Goths allied with Rome, demands a third of Italy from Orestes, but is rebuffed. The same day, Romulus meets the general of the Nova Invicta Legion, Aurelianus Caius Antonius, called "Aurelius".

The night after Romulus is crowned, Rome is attacked by the Goths. Most of Aurelius's men, pledged to protect the emperor, are killed, though Aurelius is only stunned and left for dead. Orestes and his wife are killed by Odoacer's lieutenant Wulfila, who captures Romulus.

The next day, Odoacer, now ruler of the Western Empire, plans to have Romulus killed. However, Ambrosinus convinces Odoacer to spare the boy. Instead, Romulus is exiled to Capri along with Ambrosinus, guarded by Wulfila and his men. His prison is a villa constructed more than four centuries earlier by the emperor Tiberius.

With Ambrosinus's help, Romulus discovers a hidden chamber within the villa. He comes across a statue of Caesar holding the fabled sword, forged by a Chalybian smith after his military campaigns in Britain. Writing near the statue's feet proclaims the sword was made for "he who is destined to rule". This is interpreted as a prophecy by various characters, and Romulus keeps the weapon.

The two are rescued from Capri by the loyal Aurelius and three surviving legionaries, Vatrenus, Batiatus, and Demetrius, accompanied by a female agent of the Eastern Roman Empire – an Indian warrior named Mira. They take Romulus to a seaport where the Eastern Roman Empire's emissary (whom Mira works for) and the senator Nestor have promised safe passage to Constantinople. However, they barely escape after they learn the Senate and the Eastern Empire have betrayed them and sided with Odoacer.

Ambrosinus persuades Romulus to seek refuge in Britain, where the Ninth Legion (called the Dragon Legion) may remain loyal, being far from the events. They are followed by Wulfila and his men; the Goth covets Caesar's sword after learning the prophecy. Crossing the Alps and the English Channel, the party travels to Hadrian's Wall and initially find no evidence of the legion until a farmer approaches and reveals he was its commanding general. With the collapse of Roman support of Britain, the legion had decided to disband and settle as farmers. Most of the men in the legion had married and had families. They also did not want to antagonise the powerful warlord Vortgyn. During their stay in the small Celtic village, Romulus meets and befriends a young girl named Igraine. Aurelius and Mira practice swordfighting and become close to each other. Ambrosinus told Romulus of a scar on his chest, similar to the design on the sword hilt, which he received from Vortgyn after he refused to tell him where the sword of Caesar was.

Vortgyn also desires the sword of Caesar as he aspires to rule the whole of Britain. It is revealed that Vortgyn and Ambrosinus are old enemies. After meeting with the Goths, Vortgyn decides to either capture or kill Romulus as a gesture to Odoacer. After confronting Igraine outside of the village, he convinces her to tell everyone in the village to surrender Romulus and has several of his men kill the blacksmith's wife and sons. When a tearful Igraine tells the villagers of what has happened, Aurelius confesses that Romulus is the emperor of Rome. The blacksmith then demands revenge on his wife's and sons' deaths, and Aurelius and his men decide to lead an army to Hadrian's Wall to face Vortgyn's armies in one final battle.

Before leaving the village, Romulus receives from Igraine a suit of Roman armour which belonged to her brother, which he has since outgrown. Aurelius, wielding Caesar's sword, leads his men and a small number of Celtic warriors against Vortgyn's forces at Hadrian's Wall. Mira, Batiatus, Demetrius, Romulus, and the archers pelt the infantry with arrows, while Aurelius, Vatrenus, and several Celtic soldiers struggled to hold the charging enemy at the open gate. Despite their casualties, Vortgyn's soldiers began to slowly overwhelm the small force on the wall. The battle appears hopeless until the rest of the Ninth Legion, having taken up their old Roman arms and uniforms, appear on the nearby ridgeline, and turn the tide of battle. The two warring sides cease their hostilities upon sighting Ambrosinus holding aloft Vortgyn's golden mask, after confronting and burning him alive at a tree-sanctuary of his secret brotherhood close to the battlefield.

After having fought and severely injured Aurelius, Wulfila is confronted by Romulus who is armed with Caesar's sword. Romulus stabs Wulfila in the chest, saying "that's for my mother", pauses, and further impales him, saying "that's for my father". He tells Aurelius that he fought like a dragon, whereupon Aurelius replies that Romulus fought like the son of a dragon.

Repulsed by the deaths in the battle, Romulus heaves away his sword which remarkably pierces a large rock and becomes lodged there. Many years later, Ambrosinus, now known by his Druid name, Merlin, takes a young boy to the battlefield to describe the now legendary events. Merlin, who has visibly aged little since the battle, says that Aurelius married Mira and the two raised Romulus as their own son. He became a wise ruler, took the girl Igraine as his wife, and adopted the name "Pendragon". The boy, Arthur, recognises Romulus as his father and Igraine as his mother.

In a final scene, the sword of Julius Caesar is shown embedded in the stone, with moss growing on the blade, covering the original inscription, leaving only the Latin letters which, when read as a single word, read Excalibur.

• Colin Firth as Aurelius
• Thomas Brodie-Sangster as Romulus Augustulus/Pendragon
• Ben Kingsley as Ambrosinus/Merlin
• Aishwarya Rai as Mira
• Peter Mullan as Odoacer
• Kevin McKidd as Wulfila
• John Hannah as Nestor
• Owen Teale as Vatrenus
• Rupert Friend as Demetrius
• Nonso Anozie as Batiatus
• Harry Van Gorkum as Vortgyn
• Robert Pugh as Kustennin
• James Cosmo as Hrothgar
• Alexander Siddig as Theodorus Andronikos
• Murray McArthur as Tertius
• Iain Glen as Orestes
• Rory Finn as Young Arthur
• Alexandra Thomas-Davies as Ygraine
• Ferdinand Kingsley as Young Ambrosinus

The film's producers include Dino De Laurentiis, Martha, his second wife, and Raffaella, his daughter by his first wife. Raffaella suggested director Doug Lefler due to his work on Dragonheart: A New Beginning, which she produced. Filming took place in Tunisia and at Spiš Castle in eastern Slovakia in 2005.

Valerio Massimo Manfredi helped adapt his novel to the screen, also acting as historical consultant. In an interview he states at least four hours of footage was shot but ultimately shortened or cut, including scenes of the heroes' journey through the Alps and the English Channel.

For the role of Aurelius, executive producer Harvey Weinstein suggested Colin Firth, known for playing Fitzwilliam Darcy in Pride and Prejudice (1995) and more recently, Mark Darcy in the Bridget Jones films. Firth accepted the role due to the story, which he liked, and that it was very different from previous roles.

Thomas Sangster (Romulus) was one of the last to be cast. He had previously worked with Firth in Love Actually (2003) and Nanny McPhee (2006), and their familiarity with each other benefited both.

Sir Ben Kingsley was cast as Ambrosinus/Merlin after one meeting with Lefler. Kingsley was drawn to the mystique of the character, whom Lefler describes as a "warrior shaman". Kingsley also found the story interesting.

Aishwarya Rai was cast as Mira after the filmmakers decided "somebody that had a rare beauty... who could move very well", in Lefler's words, was ideal for the role. Lefler touted Rai's training in dance as an asset for her fight scenes. Like Firth, Rai took the role as a change of pace from her previous work.

The film's costumes were designed by Paolo Scalabrino, who had worked on Gangs of New York and Troy.

Lefler wanted each character to have a unique fighting style. Richard Ryan served as the film's sword master, helping him plan the fight scenes; he had worked on Troy and would work on Stardust as such.^[3]

The film's score was composed by Patrick Doyle.

The film had a relatively poor reception by the public and critics. As of June 2010, the film had an average score of 37 out of 100 on Metacritic based on 12 reviews.^[5] On Rotten Tomatoes, 16% of critics gave the film positive reviews, based on 55 reviews (9 "fresh", 46 "rotten"). The site's consensus reads, "With miscast leads and unoriginal, uninspired dialogue, The Last Legion pales in comparison to the recent cinematic epics it invokes."^[6]

The film departs from the novel in several ways; so much so that its credits state it to be "based in part" on the original.

In the novel, Aurelius (called Aurelianus Ambrosius Ventidius) is a low-ranking officer and a legionary rather than a general, and his original legion, the Nova Invicta, is destroyed much earlier. The Nova Invicta Legion was known as the Emperor's Imperial Guard in the film, but in the novel it is a new legion formed by Flavius Orestes himself to defend the Western Roman Empire's frontiers from barbarian attacks.

The novel's band of heroes includes three surviving legionaries (Aurelius, Vatrenus and Batiatus), a Venetian warrior woman called Livia Prisca, and two Greek gladiators, Demetrius and Orosius. The film turns Livia into the Indian Mira, and Demetrius and Orosius into legionaries. While Demetrius remains a prominent supporting character, Orosius becomes an uncredited background extra.^[7]

The film alters the capital of the Western Empire from its historical location at Ravenna, as depicted in the novel, to Rome. By 460, Rome had not actually been the capital of the empire for nearly 200 years.

In the film, Romulus told his mother that "during the last five years, there have been five emperors and all of them were murdered". The five Roman Emperors Romulus mentioned were possibly Libius Severus (461–465), Anthemius (467–472), Olybrius (472), Glycerius (473–474), and Julius Nepos (474–475). While Libius Severus and Anthemius were in fact murdered by the Germanic-Roman general Ricimer, Olybrius died of an illness and both Glycerius and Nepos were deposed. Glycerius was forced to surrender to Nepos in 474, to which Nepos spared his life and sent him into exile possibly in Dalmatia. Nepos ruled over the Western Empire for thirteen months before he was deposed by the Roman commander Orestes and was forced to flee to Dalmatia.

The film depicts the coronation of Romulus (and subsequent fall of