In 1869,
Cosima Van Bulow gave birth to
Richard Wagner's son shortly before her pianist husband obtained a legal divorce from her. Wagner and Cosima were married soon after that, and Wagner
composed a piece for her, her birthday (on
Christmas) and their new son which was played on Christmas morning of that same year.
Siegfried Idyll is scored for small chamber orchestra; the orchestra which performed it was secretly rehearsed by Hans Richter, who played the thirteen bar
trumpet part in the actual performance conducted by Wagner himself. Early that day they all assembled on the steps of the Wagner
villa and began playing as Cosima, her children, and
Friedrich Nietzsche came downstairs; Nietzsche was a houseguest at the time.
Wagner had originally intended this piece as a
string quartet, it began as sketches for such and motivically holds strong resemblance with the third act of
Siegfried the opera.