Because Robert Powell looked so much like Jesus in pictures, every time he exited his dressing room in costume, the foul language the crew was using would suddenly stop.
While shooting in Tunisia, the set had a surprise visit by R2-D2. George Lucas was shooting Star Wars: Episode IV - A New Hope (1977) at the same time and, according to actress Koo Stark: "Operated by remote control, R2-D2 had to trundle off camera and disappear behind a sand dune. But the remote control failed to stop the robot and he wandered onto the set of Jesus of Nazareth."
Rarely during the movie do any of the actors portraying Jesus blink their eyes. Writer and director Franco Zeffirelli decided on this as a means of creating a subconscious visual mystique about the character that not only differentiated him from all of the other characters, and is eerily effective. The boy Jesus in the Temple blinks twice in the Temple, and the adult Jesus blinks only once on film.
The eye make-up for Robert Powell consisted of a thin line of dark blue eyeliner on the upper lid of the eye, and a thin line of white eyeliner on the lower lid. This had the effect of highlighting the piercing blue of his eyes, thus giving him a penetrating stare, when combined with very little blinking, made the character appear surreal and supernatural.
Robert Powell went on a near starvation diet (eating just cheese) for twelve days prior to shooting the crucifixion scenes in order to appear physically emaciated following Jesus' imprisonment and torture.