Sally Field in "Lincoln." (HO)

Actress Sally Field packed on 25 pounds (11 kilograms) to play former U.S. President Abaraham Lincoln's wife Mary Todd in Steven Spielberg's new film.

The Forrest Gump star portrays America's 16th First Lady and mother of four in upcoming war drama Lincoln, and in order for the project to look authentic Field was forced to gain quite a bit of weight.

The 65-year-old tells CNN.com, "I gained 25 pounds - she was much heavier, or more round, so we tried to replicate her measurements. We had her dress size, because it's documented when they made dress(es) for her... We replicated what she was, and it wasn't easy. It was sort of horrifying to be a woman of a certain age and to put on 25 pounds."

Field insists she wouldn't have transformed her body for any director other than Spielberg, who helped the actors get into character by ordering the cast and crew to dress up in period garb.

She adds, "The crew, I never saw them. I never heard them. They were quiet and they dressed in period costume. (Spielberg) dressed in a suit and jacket and tie so that you never felt invaded in your psyche that you were really in a contemporary world and you had to like, focus to try and get back into this mid 1800s. It was such a gift... He's an exquisite artist and this is his masterpiece I believe."