William (Matt Damon) is a European mercenary, who, along with a group of other mercs, want to obtain "black powder" from China. It's something that is very protected because it's so dangerous. After he and his men are attacked by some type of monster only one of his companions, Tovar, remains. The next day they are chased by a tribe until they come to a great stone wall guarded by hundreds of Chinese warriors. They are taken captive and explain their situation, though the they don't trust them at first. There's also another European there, Ballard (Willem Dafoe), who tried obtaining the black powder twenty years earlier and was never able to leave. William hits it off with Commander Lin Mae-and after the wall is attacked by thousands of the dragon-like creatures, decides to stay and help destroy them. However, Tovar has other ideas and decides to steal the black powder and leave with Ballard.
The monsters here are pretty unique looking, sort of like dragons, but with eyes in the wrong place. They are also linked together, like a hive of insects, ruled by a much larger and different looking queen. When the warriors talk about the origins of the monsters they tell of a meteor that crashed into a mountain a thousand years earlier. Yes, these are aliens. Although there are some predictable bits the film is far better than the previews suggested. Recommended.