Shen Pei
Only a few weeks after the siege mounds and tunnels were constructed, Cao Cao changed tactics and ordered them destroyed. In their place, a shallow moat 40 "li" long was dug surrounding the city. At first the moat was shallow enough to be crossed, so Shen Pei laughed when he saw it and paid it no heed. Then, in a single night, Cao Cao dug the trench further, 20 feet wide and 20 feet deep, drawing water from the nearby Zhang River to the west and encompassing the Yanpi Marsh (晏陂澤) to the south and the Huan River to the east and north. The city became isolated, and by the beginning of autumn it was said that more than half in the city died of starvation.