Suites for small instrumental ensembles, written specifically to entertain, divertimentos in the 18th century were often played as background music at upper-class banquets -- classical Muzak, so to speak -- and so their specific gravity tended to be fairly light.  Most of Mozart’s divertimenti, though unfailingly well-bred, are thus of no great musical consequence, but from time to time he turned out a large-scale piece of real expressive depth;  his Divertimento No. 15 in B Flat, composed in 1777 for the Countess Lodron of Salzburg, is an exquisite work for strings and two horns which has long been admired by connoisseurs.  Among them was George Balanchine, who called it “probably the finest [divertimento] ever written.”

Balanchine's Divertimento No. 15 is a plotless ballet in five movements (the second of the score's six minuets was not choreographed).  It contains starring roles for five women, two of whom are slightly "more equal" than the others but all of whom receive ample opportunities to shine, including sharply characterized solo variations in the second movement.  Why five women?  The answer, as usual with Balanchine, is in the music:  Mozart treats the first-violin section as a larger-than-life “soloist” which plays elaborate unison lines and, in the slow movement, collectively “sings” an aria whose sublimely poised melody is spun out endlessly, like the silvery web of a celestial spider.  Especially in the slow movement, Balanchine uses his five women in a comparable manner, bringing them out one by one to dance a seamless chain of duets that has the effect of an extended adagio for a single super-couple.

No Balanchine ballet can be explained completely by its score, and Divertimento No. 15, in keeping, contains a touch of mystery:  the five principal women are partnered by only three men.  This turns Divertimento No. 15 into a subtle study in asymmetry and, once again, it is in the slow movement that Balanchine pulls the rabbit out of his bottomless hat.  At movement’s end, the climactic duet is suddenly interrupted by the appearance on stage of the other principal dancers.  The eight principals weave among each other gracefully, accompanied by a delicate cadenza for two violins;  they then line up facing one another, five against three, and back slowly into the wings as the full orchestra brings the movement to a hushed and serene close.