A 10-meter-long section of a ditch has been cleaned up. It is 30 centimeters to one meter wide and 20 to 80 centimeters deep. Wang Lumao, head of the Sichuan provincial archaeological team, said the three ditches were abandoned during the Ming Dynasty (1368-1644), but the date of building is yet to be determined.

Wang ruled out the possibility that the ditches were used for irrigation, saying that they were likely used for drainage of urban waste water or water supply. The ditches might also be part of other urban infrastructure facilities.

Experts say that the discovery of the three ditches has provided evidence that the site where archaeologists are conducting the fourth excavation is the central urban area of the ancient Shu kingdom some 4,000 years ago.

Sanxingdui, covering an area of 12 square kilometers, is located near Guanghan City on the Chengdu Plain. It might be the ruins of the largest oriental city in the world, which dates back to between 2,875 and 4,070 years ago, according to experts.

The city walls, about 2,600 meters in length, with an average height of three to five meters, were founded around this area in an excavation in 1996. Archaeologist Chen De'an said the current excavation aims to find the urban center of the ancient kingdom, and make clear the distribution of residential areas, workshops, tombs and palaces.

A great number of potsherds belonging to different historic periods have been unearthed at the site since the current excavation started on December 4. The three previous excavations were conducted in 1929, 1986 and 1995.

(Eastday.com December 12, 2000)