File photo shows the drainage system 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. [Photo/Xinhua]

File photo shows a part of a jade crown excavated in the Pingliangtai Ancient City ruins in Huaiyang, Central China's Henan province. [Photo/Xinhua]

File photo shows a panoramic view of the Pingliangtai Ancient City ruins in Huaiyang, Central China's Henan province. [Photo/Xinhua]

File photo shows the pottery bowl excavated in the Pingliangtai Ancient City ruins in Huaiyang, Central China's Henan province. [Photo/Xinhua]