In north-central Mongolia, archaeologists have unearthed two lavish tombs built for nobles of the Xiongnu Empire. A nomadic people who dominated the eastern Eurasian steppes from the third century B.C. to the first century A.D., the Xiongnu frequently waged war against China's Han Dynasty (206 B.C.– A.D. 220). To defend against these incursions, the Han built fortifications that eventually became part of the Great Wall. Both of the Xiongnu tombs, which were excavated by a team from Ulaanbaatar University and the Henan Provincial Institute of Cultural Heritage and Archaeology, contained sumptuous grave goods. In the larger tomb, researchers found wooden...