PHILADELPHIA — Casual observers might suppose that mega-galleries like Larry Gagosian’s and David Zwirner’s are a distinctively 21st-century phenomenon. But the gallery of Paul Durand-Ruel, the Paris dealer who put Impressionism on the international map, preceded them by more than a century and a half. His fascinating and instructive story is the subject of “Discovering the Impressionists: Paul Durand-Ruel and the New Painting,” a gorgeous exhibition at the Philadelphia Museum of Art here.

This show presents more than 90 paintings, including many Impressionist works that haven’t been seen in the United States in decades or ever, all of which passed through Durand-Ruel’s hands at some point. The paintings alone make the show a popular draw. But it’s the tale of Durand-Ruel’s career, richly detailed in essays by scholars in the exhibition catalog, that makes this more than just another crowd-pleaser.