Les Troyens was an opera composed by Hector Berlioz.
Captain Jean-Luc Picard listened to the aria "Vallon sonore" from this opera in his ready room aboard the USS Enterprise-E in 2373. (Star Trek: First Contact)
The precise version listened to by Picard is contained in the complete 1969 studio recording of the opera by the Orchestra and Chorus of the Royal Opera House, Covent Garden, conducted by Sir Colin Davis and issued on compact disc ASIN B0000040Y0, September 10, 2002 on Disc 4, Track 1: Les Troyens: Act V, No. 38 - "Vallon Sonore" (featuring tenor Ryland Davies) at approximately 3:30 into the track.