The Ballet Russes is more than just a storied ballet company from early 20th-century Russia. It defined an era and aesthetic, mingling East with West, and this summer it’s getting a massive exhibit at the National Gallery of Art in Washington, D.C. Founded by Serge Diaghilev in 1909, the company was a cocktail of crossover collaborations — common today, not so much then. So among the exhibition finds you’ll discover everything from costumes by Henri Matisse, Coco Chanel and Pablo Picasso to Giorgio de Chirico set designs and illustrations by Léon Bakst and Jean Cocteau.