"We think they are the mausoleums of a king and his queen, but further studies are needed to make sure of the occupants' identities," Xin says.

"The layout of the tombs reflects typical styles of high-level residents of that time. The tombs' occupants probably had a house with three yards in their lifetimes as well."

The king may have wanted to enjoy an equally cozy existence even after death, which is why the tomb complex has front doors, columns and even windows made of clay. The exquisite frescoes found in the coffin chambers are still being restored by archaeologists. Images of deities and warriors are also visible.

Xin says five of the 16 kingdoms once existed on the plains on which Xi'an is also located. But no direct evidence like an epitaph has been found yet to connect the site to any specific state. However, based on studies of 68 unearthed funerary objects, including clay figurines, gold foils, copper coins and silver decorations, Xin suggests the tombs are from the Former Qin (351-394) or Later Qin (384-417) periods.

The two kingdoms have the same name but are distinguished by historians-Former Qin, the strongest among the 16 kingdoms, which briefly united northern China, was established by the Di ethnic group, possibly early Tibetans. Later Qin was founded by ancestors of today's Qiang ethnic group. Both kingdoms once had their capitals in Xi'an, known as Chang'an in ancient times.