MADRID, Spain -– A chance discovery of a medieval clay oven has revealed that Moorish architects used powdered animal bones to protect the walls of fortresses close to the Alhambra Palace in southern Spain.

The finding represents the first evidence of powdered bones being used in protective coats, or patinas, in Moorish architecture, said Granada University geologist Carolina Cardell, who headed a yearlong scientific research project at the site.

"We know this method was used in Greek, Roman and Celtic structures, but this is the first report of it in a Moorish building," Cardell told The Associated Press.

Cardell's team's findings were published Wednesday in the U.S. journal Analytical Chemistry.