A nobleman's tomb, coded M1902, at the Liulihe Site. CHINA DAILY

According to Wang Jing, the lead archaeologist from the Beijing Institute of Archaeology, recent excavations confirmed the existence of a second layer of city walls and moats.

The outer city wall is located about 350 meters north of the previous northern boundary, and is between 6 and 9 meters in width. The moat is between 3 and 5 meters from the wall, with an average width of 7 to 8 meters. Though many parts of the moat have been eroded by a nearby river, the surviving 1,020-meter section has already amazed archaeologists.

"Based on the position of the outer moat, it is estimated that the city could reach a square kilometer in size," Wang says. "It surpasses our current understanding of the complexity of Western Zhou cities."

New knowledge has also come from the inner city, which it is estimated covers 600,000 square meters. Recent discoveries include large-scale rammed earth building foundations spread across 2,300 sq m, and which is larger than similar findings in China from the time, as well as wells, some of which are over 10 meters deep.

"They may provide clues to the different urban functional zones of the city," Wang explains.

The 82-degree orientation of both the inner and outer cities also turns out to be identical to the newly excavated city ruins of Zhouyuan Site in Shaanxi province, capital of the Zhou Dynasty (c. 11th century-256 BC).

"They are the only two known city ruins from the Western Zhou period with multiple layers of city walls," Lei Xingshan, an archaeology professor at Beijing Union University, says. "The identical orientation and complicated structure indicate the existence of a rigid ritual system."