"Glass was a campfire legend," DiCaprio says, "and it's all true! He survived a savage bear attack, was left for dead, then travelled through this uncharted territory of interior America, crawling through hundreds of miles of wilderness on his own."

Leonardo on set with director Alejandro G. Inarritu

The story had been circulating around Hollywood for years, but filmmakers were daunted by how difficult it would be to shoot the movie in an isolated location covered in snow and ice. And indeed, as DiCaprio says, "It was epic in every sense of the word! I can name 30 or 40 sequences that were some of the most difficult things I've ever had to do, whether it's going in and out of frozen rivers, or sleeping in animal carcasses, or what I ate on set, or enduring freezing cold and possible hypothermia constantly."

To shoot the film, Inarritu took his cast and crew to remote locations in the Canadian Rockies. But the bitterly icy weather shifted, and it turned out to be the hottest year in recorded history there. "Twice during the movie we had seven feet of snow melt in a day - all of it, within five hours - and we were stuck with two or three weeks of no snow in a film that's all snow," DiCaprio says. "So we had to go to the South Pole! We had to go to the southern tip of Argentina, to the southernmost town on the planet, to find snow."

And DiCaprio says the effort was worth it, because the finished film is "epic poetry, an existential journey through nature, and this man finding a will to live against all odds. Yet he changes, nature changes him, and I think those elements changed us while we were doing the movie."

Watch the trailer for The Revenant here: