The musical score was composed by Sergio Leone’s longtime collaborator Ennio Morricone. The film’s long production resulted in Morricone’s finishing the composition of most of the soundtrack before many scenes had been filmed. Some of Morricone’s pieces were played on set as filming took place, a technique that Leone had used for Once Upon a Time in the West. “Deborah’s Theme” was written for another film in the 1970s but was rejected; Morricone presented the piece to Leone, who was initially reluctant to include it, considering it too similar to Morricone’s main title music for Once Upon a Time in the West. The score is also notable for Morricone’s incorporation of the music of Gheorghe Zamfir, who plays a pan flute. At times this music is used to convey remembrance, at other times terror. Zamfir’s flute music was used to similarly haunting effect in Peter Weir’s Picnic at Hanging Rock (1975). Morricone also collaborated with vocalist Edda Dell’Orso on the score. [Wikipedia]