The Grand Canal, known to the Chinese as the Jing–Hang Grand Canal, a UNESCO World Heritage Site, is the longest canal or artificial river in the world. Starting in Beijing, it passes through Tianjin and the provinces of Hebei, Shandong, Jiangsu, and Zhejiang to the city of Hangzhou, linking the Yellow River and Yangtze River. The oldest parts of the canal date back to the 5th century BC, but the various sections were first connected during the Sui dynasty. Dynasties in 1271–1633 significantly restored and rebuilt the canal and altered its route to supply their capital. The Grand Canal played a major role in reunifying north and south China. The canal was built by conscripted laborers and connected the Yellow River in the north with the Yangtze River in the south, which made it much easier to transport grain from the south to the centers of political and military power in north China.