By the Yuan dynasty, the configuration and function of the Grand Canal had undergone marked changes from those of earlier periods. Much of the canal system from former dynasties had become choked with silt and rendered unusable. The surviving segments—such as the Han Canal between the Yangtze and Huai Rivers, the Imperial Canal in Hebei, and the Jiangnan Canal near Tai Lake—had become fragmented and disconnected, unable to constitute an integrated transportation network. Although the Yuan dynasty still made use of these vestiges of earlier waterways, their role and significance had fundamentally shifted.