In this telling, the army is massacred in an ambush. A small band of Romans survive, and are pursued across a wintry highland landscape by Pict riders, creating one long, breathless chase.
"Centurion" has been described as a knockoff of "Apocalypto" and "Gladiator," and it's true that director Marshall is a lusty borrower (the movie is also very "Lord of the Rings" in its use of landscape).
Marshall, who grew up watching Hollywood westerns, also bites off a chunk of "Butch Cassidy and the Sundance Kid." The fleeing soldiers are bedeviled by a tracker (Olga Kurylenko) of almost supernatural skill, and when they are pushed at last to the edge of a cliff, they escape by leaping suicidally into a gorge of rushing water.
So he steals from the best, with the best, but Marshall ("The Descent") is also a talent in his own right. His movies (also "Dog Soldiers") have vivid atmosphere, energy and momentum. He's comfortable with ensemble casts, and works successfully with actors (Dominic West, Michael Fassbender) to define characters with a few bold strokes.
"Centurion" must establish its characters quickly, because it kills them just as fast. Fassbender plays a surviving officer who inherits a small band of soldiers and tries to lead them south to safety.
Without, it must be said, a great deal of success. The movie's distinguishing feature is its grim fatalism, rare for a pure action movie. We come to realize that in this bleak and brutal frontier world, there will be nothing that will look, to our modern eyes, like a happy ending.