Orfeo ed Euridice was first performed at the Burgtheater in Vienna on 5 October 1762, in the presence of Empress Maria Theresa.
The opera is the most popular of Gluck's works and was one of the most influential on subsequent German operas.
The beautiful melody comes from act 2 of the opera and is played as a flute solo. Here is an arrangement for cello and string orchestra.
The PDF file contains the score and all instrumental parts.