Lore holds he still prowls the ruins.

One version of his story says that, upon realizing the inevitability of defeat, Khara Bator killed his family and then himself.

In an alternative take, he fought to the bitter end.

And, in yet another, he escaped through the fortress' wall.

Supporters of the escape theory point to a manmade passage bored into the 9-meter-high, nearly 4-meter-thick outer bulwark that's large enough to accommodate such a stunt.

Genghis Khan's grandson, Kublai Khan, who founded the Yuan Dynasty (1271-1368), increased the strategic outpost's size threefold.

But it was abandoned when Ming troops again diverted the Ejin.

The fact that Khara-Khoto was hundreds of kilometers from, and years since, habitation meant it was all but forgotten until early last century.

Russian explorers had heard whispers of this city deserted in the desert and staged an expedition to see if the myths were true.

They excavated thousands of Tangut texts, Buddhist artifacts and woodcuts in 1908 and 1909.

Other foreigners followed-from Sweden, the United States, Britain and Japan.