The film was made under extremely difficult conditions. External sets in Nice were badly damaged by natural causes, and exacerbated and compounded by the theatrical constraints during the German occupation of France during World War II. The film was split into two parts because the Vichy administration had imposed a maximum time limit of 90 minutes for feature films.
Noted critic Pauline Kael wrote that, allegedly, "the starving extras made away with some of the banquets before they could be photographed". Many of the 1,800 extras were Resistance agents using the film as daytime cover, who, until the Liberation, had to mingle with some collaborators or Vichy sympathisers who were imposed on the production by the authorities. Alexandre Trauner, who designed the sets, and Joseph Kosma, who composed the music, were Jewish and had to work in complete secrecy throughout the production.
The set builders were short of supplies and the camera crew's film stock was rationed. The financing, originally a French-Italian production, collapsed a few weeks after production began in Nice, due to the Allied conquest of Sicily in August 1943. Around this time, the Nazis forbade the producer, André Paulvé, from working on the film because of his remote Jewish ancestry, and the production had to be suspended for three months. The famed French film company Pathé took over production, whose cost was escalating wildly. The quarter-mile long main set, the "Boulevard du Temple", was severely damaged by a storm and had to be rebuilt. By the time shooting resumed in Paris in early spring of 1944, the Director of Photography, Roger Hubert, had been assigned to another production and Philippe Agostini, who replaced him, had to analyze all the reels in order to match the lighting of the non-sequential shot list; all the while, electricity in the Paris Studios was intermittent.
Production was delayed again after the Allies landed in Normandy, perhaps intentionally stalled so that it would only be completed after the French Liberation. When Paris was liberated in August 1944, the actor Robert le Vigan, who was, ironically, cast in the role of informer-thief Jéricho, was sentenced to death by the Resistance for collaborating with the Nazis, and had to flee, along with the author Céline, to Sigmaringen. He was replaced at a moment’s notice by Pierre Renoir, older brother of French filmmaker Jean Renoir and son of the famous painter, and most of the scenes had to be redone. Le Vigan was tried and convicted as a Nazi collaborator in 1946. One scene featuring Vigan survives in the middle of the second part, when Jericho snitches to Nathalie.
Carné and Prévert hid some of the key reels of film from the occupying forces, hoping that Paris would be liberated by the time the film was completed.
Baptiste's father is played by mime and mime theorist Etienne Decroux, who was Jean-Louis Barrault's teacher (as well as Marcel Marceau's). Many of his character's lines about theatre can be interpreted as ironic statements on his own work in corporeal mime.
After the film was made, accusations of collaboration made against Arletty were met with her classic response : "My heart is French but my ass is international."
Source : Wikipedia.