Every day during filming, Errol Flynn would drive on the Warner Bros. lot wearing a windbreaker with no shirt, slacks with no underwear and shoes with no socks. The wardrobe people would provide him with a shirt, underwear and socks, and at the end of the day's filming he would wear them home. The next day he would arrive on the lot, again with no shirt, underwear or socks, and again he would be supplied those items by wardrobe. Co-star Paul Picerni noticed it after several days, and asked Flynn what he did with all the shirts, socks and underwear he'd accumulated after several weeks of filming. Flynn replied that he threw them in a closet when he got home. Picerni asked, "But what do you do with them?" Flynn replied, "Nothing. It just gives me pleasure to steal from [Jack L. Warner].
According to production notes from the Warner Bros. studio archives, Raymond Burr lost 120 pounds for this role; Ruth Roman had to be hospitalized with an arm injury; Errol Flynn burned his face during the fire sequence.
The jeweled cross was made by noted Beverly Hills jeweler David Zakwin and his sons.
The short sleeve collared knit shirt Errol Flynn wears was not yet mainstream fashion for men in the U.S. Although the famous Chemise Lacoste polo shirt had been around since 1933, it was largely worn as sport or vacation attire. In a few decades, the polo shirt would become ubiquitous.
The beautiful Mission San Fernando Rey, at the far north end of what is now the greater Los Angeles San Fernando Valley, stood in for the cathedral at Manila. Both California and the Philippines have Spanish colonial architectural history.