John Wayne broke his leg during filming.
The Bible text, "And they shall go into the holes of the rocks, and into the caves of the earth, for fear of the LORD, and for the glory of his majesty, when he ariseth to shake terribly the earth. / In that day a man shall cast his idols of silver, and his idols of gold, which they made each one for himself to worship, to the moles and to the bats...", is from Isaiah, chapter 2 verses 19-20.
The part of Bonnard was first offered to James Mason.
The Spanish title for this film was "Arenas de Muerte", which literally translates to "Sands of Death". The Spanish poster only features a closeup of the face of Sophia Loren and her name comes above John Wayne's. She was a much bigger star in Spain than Wayne was in 1957.