Measuring 26 feet by nine feet, it is an outsized testimony to Raphael’s talents.

“There are details in the cartoon, sketched in charcoal, that are remarkable for their originality,” Antonella Ranaldi, Milan’s principal official in charge of art and archaeology, said at a news conference on Monday. “It is a precious testimony,” she said.

Its value must have been evident to Raphael’s contemporaries, and rather than use the cartoon itself for the fresco, a copy was used and the original was preserved. That copy was destroyed through use when the outlines of the figures and details were pricked with pins, and the cartoon was dabbed with a cloth bag containing charcoal powder to transfer the image to the walls