Donald Sutherland got so upset after seeing his own performance as the sadistic homicidal fascist leader Attila that he was unable to watch the film for years.
The original uncut version is five hours and seventeen minutes long, and features additional dramatic scenes, actual animal killings, and explicit sex scenes including one involving Alfredo, Olmo, and Neve.
Bernardo Bertolucci stated that in an interview, he filmed the scenes of the movie based on the four seasons. If you notice, the meeting of the boys is summer, the adult reunion of Alfredo and Olmo takes place in a fall moment. The Fascist takeover is winter, while the end of World War II is spring.
Bernardo Bertolucci himself cut the three and a half hour version that was originally shown internationally, which he did to appease the studios and financiers, who wanted to use an even shorter cut, that was never released. He still says he prefers the original five hours and seventeen minute cut. His main complaint with the international release, was the English title "1900". With the original title "Novecento", he meant to imply a tale of the twentieth century.
Regina is supposed to be the same age as Alfredo and Olmo, but Laura Betti was 16 years older than Robert De Niro and 21 years older than Gerard Depardieu.