Most of the dialogue is overdubbed by other actors than the ones seen on screen. This is very apparent if you watch carefully at the lip sync, which can deviate wildly from the actual dialogue. The voice actors are all uncredited in the actual film.
Filming was highly problematic, as Luchino Visconti found himself continually denied promised permits, and was forced to shoot in unsuitable locations. To add insult to injury, he was forced to make some deep cuts to his finished film.