Art: Master of the Gesture

"The Age of Caravaggio," the Metropolitan Museum of Art's big show this winter, may come to be remembered as a marker in the history of exhibitions. Not even the Met, this time, could get the loan of his greatest work. Owners and curators are getting more conservative, especially in Italy, and the days when uniquely important works of art could be flown around the world like greeting cards, even for scholarly purposes, are fading.

In 1951, when the Italian scholar Roberto Longhi mounted the crucial show that brought Caravaggio's turbulent genius out of three centuries of neglect and obloquy, this was...