In the barrens of upper Britain circa A.D. 120, the occupying forces of Rome's Ninth Legion, 5,000 strong, marched north of Hadrian's Wall - and vanished. Likewise disappeared their standard, a gilt eagle, insignia of the empire.

Were the legionnaires slaughtered by the Picts, the painted and tattooed tribes living at the ends of the known earth in Caledonia, what we now call Scotland? And what happened to the Romans' precious insignia?

So begins The Eagle, a muscularly entertaining adventure inspired by Rosemary Sutcliff's historical fiction The Eagle of the Ninth, hugely popular in middle schools in the mid-20th century.

The story of an occupying army, which assumes natives will defer to its military might, has obvious parallels to American forces in Vietnam and Afghanistan.

When centurion Marcus Aquila (Channing Tatum) arrives at a Roman outpost near Hadrian's Wall 20 years after the Ninth's vanishing, he has a simple to-do list. Namely, find what happened to Dad's legion; restore family honor by recovering eagle. After a skirmish with restless Caledonians (who embed blades in chariot wheels), Marcus proves his valor.

In this collegiate version of Gladiator, director Kevin Macdonald (The Last King of Scotland) similarly has a simple to-do list. Namely: Tell the rousing prehistory of his native Scotland; show how antagonists can be allies. He succeeds on both counts. Though not deep, the movie is diverting.

While nursing battle injuries, Marcus rescues a wiry and wily Caledonian, Esca (Jamie Bell), from almost-certain death when the youth is thrown into a gladiatorial match with a combatant easily three times his size. In exchange, Esca will be Marcus' slave and accompany his new master into Caledonia on a reconnaissance mission to find the missing members of the Ninth and their standard.

The craggy landscapes (shot in Scottish Highlands and in Hungary), beautifully captured by cinematographer Anthony Dod Mantle, have more intrinsic drama than the quest of the searcher and his slave.

Much of the time Tatum and Bell resemble the captain of the college football team and the head cheerleader of the rival team locked in an uneasy alliance.

On Caledonian soil the shifting balance of power gives dimension to their flat characters. Esca can communicate in Caledonian dialect. What isn't he telling Marcus?

The film, rated PG-13 for relatively restrained combat scenes, has more of a survivalist rather than a gladiatorial thrust.

The Eagle **1/2 (out of four stars)

Directed by Kevin Macdonald. With Channing Tatum, Jamie Bell, Donald Sutherland, and Mark Strong. Distributed by Focus Features.

Running time: 1 hour, 54 mins.

Parent's guide: PG-13 (battle sequences, disturbing images)

Playing at: area theaters


Contact movie critic Carrie Rickey at 215-854-5402 or crickey@phillynews.com. Read her blog, Flickgrrl, at http://www.philly.com/philly/blogs/flickgrrl/.