At the Nanzuo site in Qingyang, Gansu province, archaeologists unearthed the ruins of a huge city dating back 4,700 to 5,200 years. A palace, whose design can be seen in imperial cities in later dynasties, and exquisite pottery may provide clues to a previously unimaginable power hub on the edge of Loess Plateau.

Han Jianye, an archaeology professor at Renmin University of China who led the excavation, said the site may have functioned like a national capital.

Wang Wei, director of the Chinese Academy of Social Sciences' Academic Division of History and a leading expert in the origins-tracing program, said, "The development of Chinese civilization has been continuous, and various roots of our civilization were linked with and frequently exchanged with others, gradually forming a shared community.

"For example, it cannot be mere coincidence that various regions had the same admiration for jade and many of their jade patterns were similar," Wang said.

"A network for communication and exchanging information probably existed among upper classes in different societies. Dragons were also commonplace in various belief systems. These factors formed the foundation for a united Chinese civilization in later history."

Although Niuheliang and Lingjiatan are more than 1,400 km apart, their jade has a high degree of similarity.

Liu Guoxiang, a researcher at the Chinese Academy of Social Sciences' Institute of Archaeology, said various types of jade had the same influential effect.

"People interacted and learned from each other, and cultures prospered as a result," he said.

"They recognized each other's values, views and morals, and provided a big picture of how people from northern and southern areas of present-day China mixed between one another."