A forgotten section of the Great Wall of China has been discovered deep in the Gobi Desert—and outside of China—researchers say. With the help of Google Earth, an international expedition documented the ancient wall for roughly 100 kilometers (62 miles) in a restricted border zone in southern Mongolia in August 2011. Preserved to a height of 9 feet (2.75 meters) in places, the desert discovery belongs to a sequence of remnant walls in Mongolia collectively known as the Wall of Genghis Khan, said expedition leader and Great Wall researcher William Lindesay. Named after the founder of the Mongol Empire, the Wall of Genghis Khan usually survives only as "a faint trace," Lindesay said in an email. The Great Wall system built by successive Chinese dynasties to repel Mongol invaders from the north, according to findings published in the March issue of the Chinese edition of National Geographic magazine.

Close to China in the border region of Ömnögovi Province, the ancient structure hadn't been scientifically explored or studied before, said Lindesay, director of the International Friends of the Great Wall conservation group, based in Beijing, China. "We're the first to investigate the ruins," he said. At times seeking out topographic clues seen in Google Earth—the wall is visible on satellite images—the team located two well preserved but contrasting stretches of wall.

Ancient Mongolian texts suggest that the so-called Wall of Genghis Khan was built as an animal fence by Khan's son Ögedei to keep wild gazelle on his land. But the recently explored Gobi Desert wall segment isn't in a region where large herds of gazelle occur. Chinese researchers, perhaps not surprisingly, have speculated that China's Han dynasty had erected these little-studied stretches in about 115 B.C. But radiocarbon dating of partly exposed wood and rope remains extracted from the wall indicates that the saxaul-segment construction went on for more than a hundred years—and occurred about a thousand years later than thought, from A.D. 1040 to 1160. Those dates hint that the Western Xia dynasty built the walls—or at least rebuilt old Han walls on the sites.

This northwestern Chinese dynasty isn't known to have contributed to the Great Wall system, but in at least one aspect, a Western Xia origin makes sense. "If one imagines the wall as a platform, with some kind of battlement—perhaps of wooden stakes, functioning as a shield to those manning its top—then it would have been an effective defense installation," he said. But, mysteriously, the expedition team found no pottery, no trash, no coins, no weapons—nothing to prove the wall was ever actually manned. Nor did they find any of the watchtowers that mark surviving sections of the Great Wall within China.

"I believe the wall here is only half built and that there was, for some reason, a rethink on locating the wall here," Lindesay said. It isn't difficult to imagine how the purported Great Wall segment's harsh desert location might have led to the remote frontier defense being abandoned, he added. Weatherford, the Minnesota-based anthropologist, agrees with Lindesay's conclusion that the newfound remains were Chinese constructions. There's a good reason, Weatherford added, that the stretch nevertheless carries Genghis Khan's name. "By calling it the Genghis Khan Wall, the name makes the place Mongolian and rejects foreign influence," Weatherford said. "I would risk saying that it is the largest human-made structure or artifact in all of Mongolia," he added. "It is amazing to me that it is not already much better analyzed."