In The New York Times, Johanna Keller traces the rise of Samuel Barber's Adagio, "arguably the most often-heard work of classical music written in the last century."
Barber, whose centenary is being celebrated this
year, composed the Adagio in 1936 as the slow movement of his String Quartet, soon enlarged it into a string-orchestra piece (its most familiar version), and then as a choral work, his Agnus Dei. Others have reworked it in many ways, but haven't altered its effect on listeners. "If any music can come close to conveying the effect of a sigh, or courage in the face of tragedy, or hope, or abiding love, it is this," Keller writes:
http://www.nytimes.com/2010/03/07/arts/music/07barber.html?pagewanted=1&ref=music
In this century, the Barber Adagio is best-known as the musical elegy for the victims of the terrorist attacks on Sept. 11, 2001. Here's the performance given shortly afterward by Leonard Slatkin and the BBC Symphony:
http://www.youtube.com/watch?v=RRMz8fKkG2g