Treatise on Military Preparedness (Vol. 98)

From the office downwards, the area reaches Laoguanzui and connects to the Yizhen Guard defense post at Qingshan Sanjiangkou. The total distance is 20 li approx. 10km. The soldiers and archers are to rotate shifts to patrol back and forth. The Xie-gou area is guarded by volunteer militia; it reaches the old river mouth of Yizhen at a distance of 35 li, and downwards it reaches the Gaozi Town Inspection Office at a distance of 40 li. That location originally had no patrol boats; there were only 40 civilian laborers. Whenever a patrol meeting occurred, they were required to hire civilian boats to go out onto the river. It has been investigated that the capital is 90 li from Jurong County. Jurong, Longtan, and Xie-gou are each 70 li apart. The Yangtze River region is segmented by islands and sandbars. Only the boat traffic at Xie-gou and Longtan goes in and out from here, therefore Huangtiandang has become a den for bandits, while Longtan and Xie-gou are the strategic transit points. For this reason, the defense of these two locations requires even more attention than other places. Now, examining Longtan: