The famous scene in the Trevi Fountain was shot in March, when nights were still cold. According to Federico Fellini (in an interview with Costanzo Costantini), Anita Ekberg stood in the cold water in her dress for hours without any trouble. Marcello Mastroianni, on the other hand, had to wear a wetsuit beneath his clothes, and even that wasn't enough. Still freezing, he downed an entire bottle of vodka, so that he was completely drunk while shooting the scene.
The film contributed the term "paparazzo" to the language. The term derives from Marcello's photographer friend Paparazzo. Federico Fellini took the name "Paparazzo", as he explained in a later interview, from the name of someone he met in Calabria (Southern Italy) where Greek names are still common. "Paparazzi" is the plural meaning.
It seems that term "paparazzo" was coined by Federico Fellini himself. Paparazzo means "sparrow" in one Italian dialect (in normal usage the Italian for "sparrow" is "passero"). Fellini explained that the photographers hopping and scurrying around celebrities reminded him of sparrows.
When shooting the famous Fontana di Trevi scene, director Federico Fellini complained that the water in the fountain looked dirty. A representative of Scandinavian Airlines System (SAS) present at the shooting was able to supply the film team with some of the airline's green sea dye marker (for use in case of an emergency landing at sea). This was used to color the water, and the director was satisfied.
The Italian catholic party Democrazia Cristiana and the Vatican were deeply against this movie for the portrayal of the city of Rome and its vicious aristocracy (which is historically very close to the Church). One article against the movie, "La schifosa vita" (The filthy life) was probably written by Oscar Luigi Scalfaro, in 1992, President of the Republic.
Asked how he got the idea for the film, Federico Fellini replied that one year the fashions made the women in Rome look like big flowers. Several extremely exaggerated costumes here and there in the film (such as two women guests' cloaks in the sequence of the party at the castle) point back to this original inspiration.
In the beach house sequence, when the woman asks Marcello if he was a 'writer once,' and Marcello announced he's now a publicity agent,' the young woman reads frm a magazine 'he has a Greek profile, but the modernity of his expression brings him to the most modern actor of our time - Paul Newman.' She reads the quote - and the actor's name with disappointment, which is an intentional sly reference to Paul Newman, as Paul Newman was Dino De Laurentis' choice for the lead - which Marcello Mastroiani eventually took.
A scene was mooted that involved Marcello's relationship with an older writer, Dolores, to be played by Oscar winning actress Luise Rainer. After much protracted discussions and difficulties, due to Luise Rainer's wish to rewrite her role somewhat, Federico Fellini cancelled the scene altogether. The actress was furious, reportedly saying, "I have spoiled a priceless piece of cloth on this character that will never be!"
The trivia item below may give away important plot points.
In the Steiner home suicide scene, the famous "Il Fungo" (The Mushroom) water tower in the EUR zone can be seen directly from his balcony. This structure is featured prominently in Michelangelo Antonioni's 1962 film "L'Eclisse" (Eclipse).