The primary mode of travel was thought to be watercraft. People even built channels as makeshift rivers to connect urban core areas to adjacent rivers or from towns to main rivers. In addition to walls, moats were also dug around towns and urban centers in the same fashion as the constructed channels. At the town site at Chengtoushan, the moat is about 40–50 m in width. Researchers estimate that a total labor force of 200,000 to 470,000 people was needed to construct the moat and walls at this site. The people of the Shijiahe culture grew both rice and millet.