Treatise on Armament Technology: Logistics for River Crossings

... ropes or vines, using iron chains original: 鐵索 (tiesuo) to link them together so they stretch across the middle of the current. Fill these structures with earth-filled bags original: 土囊 (tunang); these functioned much like modern sandbags to stifle the force of the water. Once the water level has subsided and become shallower, the various army units can cross.