Revealing mistakes: At the top of St. Peter's dome the wind blows Sylvia's hat off. The wire on her hat used to achieve this effect is clearly visible trailing off to the right during the scene.
Continuity: The aircraft which brings Sylvia to Rome is an Alitalia Vickers Viscount as it comes in to land, but is both a Douglas DC-7C and DC-6B when it is on the ground.
Continuity: When the two children see the Madonna, the time of day is stated as 7:00. However, the very short shadows of the characters reveal that it is midday.
Miscellaneous: In the castle, Marcello lights a match to view some ancestral paintings. A spotlight is used to enhance the light of this match, but does not follow the actor's movements very closely and gives the illusion away.
Audio/visual unsynchronized: The water in the Trevi Fountain continues flowing even after the sound of it has faded away, and only stops when the camera changes view.