Landscape with Hercules and Cacus

Poussin painted this in Rome around 1660, in his last years, when a tremor had crept into his hand and he had mostly set aside the crowded dramas that made his name. The subject is violent. Hercules has just killed Cacus, the fire-breathing thief who dragged stolen cattle backward into his cave so the hoofprints would point the wrong way, a tale Poussin took from Virgil. But you have to hunt for it. The killing is a small knot of figures far off, almost lost under a wide still sky and hills laid out with the care of a mathematician. A century later the philosopher Denis Diderot bought the picture for Catherine the Great of Russia, which is how a French painter's Roman landscape ended up in Moscow.