File photo shows the pottery bowl excavated in the Pingliangtai Ancient City ruins in Huaiyang, central China's Henan Province. Archaeologists have unearthed a number of pottery drain pipes at a Neolithic site of Longshan Culture dating back more than 4,000 years and believe they form China's earliest and most complete urban drainage system. The city drainage system was excavated in the Pingliangtai Ancient City ruins in central China's Henan Province. (Xinhua)
