Lincoln Kirstein called it a “full-length ballet without a plot,” but George Balanchine’s Jewels—which premiered in 1967 and consists of three acts: “Emeralds,” “Rubies,” and “Diamonds”—is a castle keep of Medieval imagery, Symbolist echoes, neoclassical refractions, and the story of Balanchine’s heart. It’s also a primer on national approaches to classical dancing: the deep lustre of French “Emeralds,” the elbowing refractions of American “Rubies,” and the cosmic grandeur of Russian “Diamonds.” The Mariinsky first performed Jewels in 1999, and it was a passionate homecoming, a company embracing its prodigal son, Balanchine—especially in “Diamonds,” with its glints of snowbound palaces and Tolstoyan ballrooms. —L.J.