Simmons' career often reads like a lesson in what might have been. She rose to early success in films such as David Lean's Great Expectations and Laurence Olivier's Hamlet (which earned her an Oscar nomination) before running afoul of her contract holder, Howard Hughes. After rejecting his advances, he attempted to ruin her career and cost her the lead in Roman Holiday. Simmons held out, and managed success with roles in Young Bess, Footsteps in the Fog, Guys and Dolls, and The Actress.
Due to financial strain, she quietly accepted any role offered, and Simmons became known as the quiet lady who supported great men in films like The Robe, The Egyptian, Desiree, Elmer Gantry, and Spartacus. She always rose above the material, and was an actress the formidable Pauline Kael championed. Kael called her "one of the most quietly commanding actresses Hollywood has ever trashed" and always hailed her performances as better than the films she was given. I think she was certainly right, as evidenced by her haunting turn in Spartacus. She's undoubtedly one of the most memorable things about the film. Even if she was not a screen legend like her Roman Holiday replacement was, she certainly made an impact.
Rest in peace, Ms. Simmons. You'll be missed.