Matt Damon defends 'The Great Wall' against claims of whitewashing "It's this crazy monster movie," he told ABC News.

 -- Don't judge Matt Damon’s latest film, "The Great Wall," by its poster, he says.

The casting of a Western actor in what appeared to be a historical film about the Great Wall of China drew controversy when it was announced. But the movie is not what you might think, Damon told ABC News.

"This was designed as a giant East-meets-West co-production creature-feature monster movie," he says. While concerns about cultural appropriation "are real and justified, in general. I would be surprised if people thought they applied to this after they saw it."

"I guess you'd say it's historical fantasy," he says of the film, which is actually about European mercenaries searching for gun powder, but who end up defending the Great Wall against a horde of monsters.

Damon blames misunderstanding about the film on early promotional images.

"Those allegations were kind of centered on the poster. And it said, 'The Great Wall,' and then it was my name and my face and people were like, 'What the...? You know, right?'" he explains. "So there was this kind of outcry, like, I think people maybe thought it was something about building the Great Wall, or something having to do with actual Chinese history."

Instead, he explains, "It's this crazy monster movie. You know, so it's 1100 A.D., but there are monsters. I guess kind of like 'Game of Thrones.'"

"The Great Wall," co-starring Willem Dafoe, opens in limited release Thursday, nationwide Friday.