The state of Bohai (698-926), founded by an ethnic tribe in northeast China, had close ties with the Han culture in the Tang Dynasty (618-907), and was influenced by the latter's government institution.
　　 The project to study the Bohai Shangjing Longquanfu Palace City Site has been carried out by the State Administration of Museums and Cultural Relics since 1997. It was scheduled to be completed within 10 years, to get a full picture of the Shangjing Longquan Palace City, the capital of Bohai, thereby providing important first-hand materials for further study of the origin of the culture of that state.
　　 From July to October 1999, archaeologists completed a large-scale excavation of the site of the palace city at Bohai Town in Ning'an, Mudanjiang city, Heilongjiang Province. The result of the excavations demonstrated that one palace at the site is almost identical in structure and style to the emperor's audience hall in the Daming Palace, the Hanyuan Hall, in the Tang capital of Chang'an. After analyzing its dimensions, the experts concluded that it was also a venue of the emperor and his ministers for discussions of state affairs. 　　Valuable cultural relics were unearthed, including a large number of tiles inscribed with Han characters, which shows that Han writing was used at the court. In addition, there is a gilded bronze statue of Buddha. At that time, Buddhism was in the ascendant at the Tang court.
　　 Two bulletin boards were found on a brick base, on which the words "four grades" and "four positions" of officialdom were inscribed. It shows that Bohai followed the Tang system of decrees and regulations. According to the available archaeological data, the bulletin boards were the first unearthed in China.
　　 The international academic community has reached a common view that the state was founded primarily by the local Mohe ethnic group. It submitted to the Tang, and its titles of nobility were conferred by the Tang rulers.