On the vast flatlands of eastern Mongolia, enclosed by a two-mile wall in the form of an oval, diggers have uncovered tantalizing clues to the solution of one of history's enduring mysteries: the site of Genghis Khan's secret grave.

Finding the spot where the great Mongolian conqueror was laid to rest in 1227 by his famed horseback warriors would fill in a blank that has fascinated historians for centuries. Although he and his descendants galloped out of Mongolia to subdue most of the known world, Genghis Khan was buried without a monument or even a headstone, in keeping with Mongol belief that the dead should not be disturbed. Legend has it that the soldiers who carried out the mission were slaughtered to make sure the secret was safe for all time.

For eight centuries it has been, despite a number of more or less scientific expeditions, claims and counterclaims, some of them evocative of an Indiana Jones movie. But a U.S.-Mongolian expedition organized by Maury Kravitz, a retired Chicago commodities trader, made what may have been a breakthrough two summers ago. His explorers unearthed several graves dating from the 13th century inside the wall, a shambles of stone 200 miles east of Ulan Bator, the Mongolian capital. Shagdaryn Bira, secretary general of the International Association for Mongol Studies and a recognized authority, said the graves are a promising sign that the wall could surround the bodies of Genghis Khan and his closest kin.