"Harriet" star Cynthia Erivo says we "need more Harriet Tubmans" on big screen

British actress Cynthia Erivo, who stars in the new film "Harriet," hopes she won't be the last to play the famous Underground Railroad conductor Harriet Tubman on a big screen. Responding to criticism about being cast over an American actress, Erivo said she understands where the critics are coming from.

"I think it's because these characters are rare," she said on "CBS This Morning" Friday. "But … I hope it just encourages more of these films because we have plenty of Abraham Lincoln, plenty of Winston Churchills. But we definitely need more Harriet Tubmans."

"Harriet," released Friday, is the first major feature film about Tubman's life, detailing her escape from slavery and how she helped free hundreds of other slaves through the Underground Railroad. Preparing for the film, Erivo said she learned how important Tubman's faith was to her.

"One thing that was really wonderful about learning about her is that she had a deep connection to her spirituality," she said. "It was really her faith — what she believes were God's directions to the way that she needed to go. And I didn't know that that was such a huge part of her story."

Learning that gave Erivo the opportunity to look at her own faith. "To go in and, you know, be a bit braver with my faith and say my prayers and really … embrace it," she said.

Erivo also had to prepare physically for the role. "The stunt work is me," she revealed. "I was working out the hour before I would get on set," she said, "so that I didn't have to play catch-up while we were doing all those things."

But the stunts don't compare to the hardships Tubman actually went through, Erivo said. "We knew that at the other end, there would be someone with a coat and we'd be able to go back inside and we were fine."