Actually "Quo Vadis" in pre-dates "The Sign of the Cross." QV is based on the classic novel by Henryck Sienkiewicz, first published in English (translated from the original Polish) in 1897. The first film version of "Quo Vadis" was the Italian silent film from 1912, considered the first epic film. So, if anything DeMille's "The Sign of The Cross" was a copy of "Quo Vadis." Sign's Nero, Charles Laughton, was first approached to repeat his role when MGM started planning to film QV in the 1940s, but the role eventually went to Ustinov.