Guangji Bridge (Guang Ji Qiao; literally 'Great Charity Bridge'), also known as Xiangzi Bridge is an ancient bridge that crosses the Han River in Chaozhou. The bridge is renowned as one of China's four famous ancient bridges; the other three are the Zhaozhou Bridge, the Luoyang Bridge and the Lugou Bridge. The Guangji was originally a pontoon bridge built in AD 1170 during the Southern Song Dynasty with a length of 518 metres (1,699 ft). Later, construction of piers and framework started from both banks of the river on which it was moored, and 200 years later the current form of the bridge, with a floating section supported by 18 wooden pontoons between two beamed sections, was completed. The floating section can be disconnected for the passage of large boats, an innovation that set a precedent in bridge-building history. Chaozhou is believed to have been founded more than 1700 years ago. The town reached its zenith during the Ming era and was well known as a place of great culture as well as an important commercial and trading centre. Teochew dialect, by which the Chaozhou culture is conveyed, is one of the most conservative Chinese dialects because it preserves many contrasts from ancient Chinese that have been lost in some of the other modern dialects of Chinese.