The first attempt to film the chariot race was on a set in Rome, but there were problems with shadows and the racetrack surface. Then one of the chariots' wheels came apart and the stuntman driving it was thrown in the air and killed. See also Ben-Hur (1959).
Producer Irving Thalberg was short of "hedonist slave girls", so he called up Hal Roach and Mack Sennett to ask a favor: to loan out their famous "Bathing Beauties". They were happy to oblige, as many girls were making their film debuts. Among the group of 20 or so girls who eventually appeared in the film: Janet Gaynor, Carole Lombard, Fay Wray and Joyzelle Joyner.
Many of the scenes in this film, interestingly enough, were NOT remade in the more popular 1959 version of the story. Among these are the three Wise Men's journey through the desert, Mary and Joseph seeking refuge in the manger, and the scene in which Messala enlists the help of Iris to discover the identity of his chariot-racing opponent.
At one point in the chariot race a man in modern clothing - light-colored shirt, long pants, dark shoes - can be seen running out of the crowd onto the track and waving his arms at the camera. That was assistant director William Wyler, who saw that one of the chariots - out of camera range - was approaching the curve of the track too fast and Wyler was signaling the director to have the crew cleaning up a crashed chariot to get out of the way.