This was originally announced in 1964 as a starring vehicle for Gregory Peck.
William Flaherty, who wrote the screenplay, was a Jesuit priest.
Anthony Quinn was on Variety's list of Top Ten Overpriced Stars of 1968.
Despite the fact that it was a European co-production and the presence of Ennio Morricone, Anthony Quinn and Charles Branson,this was actually filmed entirely in Mexico.
Takes place in 1700s Mexico then ruled by Spain