TIANJIN, June 21 (Xinhua) -- Northern China's Tianjin Municipality has discovered over 50 relic sites that spanned three millennia in the Chinese history, local archaeologists said Thursday.

The Tianjin Cultural Heritage Protection Center said after one month of excavation, they found the sites dating between the Xia Dynasty (2070-1600 BC) and Qing Dynasty (1644-1911 AD).

They are all parts of the Tangfang Site in the Jizhou District, a northern suburb of Tianjin, said Gan Caichao, a researcher with the center and head of the excavation project.

Among the newly found sites are about a dozen from the early dynasties of Xia and Shang (1600-1046 BC), where many pottery fragments, including those of cooking utensils and containers, were unearthed, according to Gan.

More than 30 tombs of commoners from the dynasties of Ming (1368-1644) and Qing are another important find in the ongoing excavation. Burial items, however, are relatively scarce in these tombs.

It is the second time Xia and Shang relics were found in Jizhou District, which declared its first such discovery in the 1970s.