The young warriors are set against the old-school Roman nobles who can't fathom how they might come to reevaluate the entire notion of empire, not to mention slavery.
Marcus Aquila (Channing Tatum) bears a heavy burden. You know this because he knits his brow and spends long minutes staring into the dark night. You also know because when he arrives to take command of a Roman outpost in rural Britain, the men mutter and explain: Marcus' dad led and lost the Ninth Legion. It's bad enough that dad lost 5,000 centurions, a number repeated frequently. It's worse, apparently, that he also lost the Golden Eagle, an emblem of Roman honor in the second century, when The Eagle takes place.
Earnest if not necessarily thoughtful, Marcus means to restore that honor -- to his empire and also to his family. If the result of his quest is predictable, the route is occasionally arduous. For one thing, that outpost he's commanding is set in a territory deemed “the end of the world” by the Emperor Hadrian, who's had a huge wall erected to mark it and make sure no more Romans get lost in it. As such border walls have a certain currency in the United States today, you'd be forgiven for imagining there's a moral lesson here, namely, walls are premised on and prolong ignorance, as well as the inevitable war-making.
It's not long before Marcus' plan goes awry. Though he proves himself to be a potent warrior during a rather daunting attack by wild-haired British Picts, he is also wounded, and so shipped off to recuperate at the home of his Uncle Aquila (Donald Sutherland). A onetime military officer now retired to a life of considerable leisure, Uncle doesn't quite get the desperation his nephew still feels about the whole honor thing. Uncle is further surprised when Marcus goes out of his way to rescue a British slave, Esca (Jamie Bell), from death during an entertainment at the local coliseum. This makes Esca Marcus' responsibility -- and property -- and as Marcus' mobility and fervor are restored, the young men engage in a montage of masculine bonding via riding, hiking, and hunting.
This sets in motion the next part of the plot, a journey past the end of the world, also known then as Caledonia and now as Scotland (which nominally connects this film with director Kevin Macdonald's previous historical fiction, The Last King of Scotland, another story of vexed relations between master and slave/worker). Here, Marcus intends to find the Golden Eagle, which someone has reported seeing somewhere. Uncle advises against the adventure, especially the trust Marcus is placing in Esca ("He's a slave: he says what he says and does what he does because he has to"), but Marcus heads off into the mist anyway, Esca in tow.
Over the wall, they run into troubles of course, mostly embodied by a Pictish tribe and especially their leader, the Seal Prince (Tahar Rahim). When this crew first discovers the trespassers, Esca (the only one who speaks both languages, the tribe's Gaelic and Marcus' English [passing for Latin here]), says he's the master and Marcus the slave, in order, he reasons, to save both their lives. This leads to yet another new experience for the Roman, who begrudges the beatings and the emotional cruelty heaped on slaves, as well as Esca's apparent betrayal.
This reversal of roles is the crux of the film's second moral lesson, related to the first. As Marcus comes to see that the Romans invade other people's lands and destroy their honor, he begins to feel something like sympathy for the victims of his empire -- at least until the Picts persist in their strangeness and ferocity. And this is the film's unresolved dilemma: even as it offers up the Roman's self-revelation (so he's a little like a U.S. officer who discovers that Iraqi or Afghan locals, say, resent him), it can't stop otherizing the enemies (as long as they're alive and painted blue, anyway). So, even as Marcus and Esca come to their own and sometimes shared revelations concerning how bad it is to beat up other races/clans/populations/classes just because you can, the Seal Prince remains a relentless force -- painted even in rainstorms, grim even when engaged in party-like rituals with his men. The Seal Prince's pursuit of the buddies Marcus and Esca over rough terrain and under harsh conditions makes him seem implacably monstrous, fully deserving his inevitable fate.
This blind spot is lamentable in The Eagle, which plainly values moral education for its protagonists and stages that education in lively fast-cut battle scenes designed to please an audience who might benefit from it. Marcus and Esca are set against the old-school Roman nobles -- including Uncle Aquila -- who can't fathom how the boys might come to reevaluate the entire notion of empire, not to mention slavery. Recovering the Golden Eagle is thus a very tricky double-edged enterprise, both imperial and anti-imperial.