In the scene where Pope Kiril I (Anthony Quinn) prays over the body of the Jewish man, he recites the Shema. However, rather than say "Adonai," he says, "Hashem." This is because "Adonai" is traditionally only said when one is actually at prayer, and not simply reciting a prayer in a secular context, as in during a performance (specifically, in a movie).
Although it is never mentioned nor indicated at any point in the movie, the story is set 20 years in the future.
Alex North re-used the opening fanfare he wrote for 2001: A Space Odyssey (1968), but which had been rejected by Stanley Kubrick, as one of the main themes in his score.
Ernest Borgnine badly wanted the role of Pope Kiril I.
The papal name of the Pope who dies during the movie is Pius XIII. It is never spoken during the movie, but can be seen etched in reverse on his papal seal before it is ceremoniously destroyed.