Book 14 · 备突 · Chapter 47
城百步一突门，突门各为窑灶，窦入门四五尺，为亓门上瓦屋，毋令水潦能入门中。吏主塞突门，用车两轮，以木束之，涂其上，维置突门内，使度门广狭，令之入门中四五尺。置窑灶，门旁为橐，充灶伏柴艾，寇即入，下轮而塞之。鼓橐而熏之。
Every hundred paces along the wall, make one sally-gate (tu-men). At each sally-gate construct kiln-stoves (yao-zao), with a duct (dou) running into the gate four or five feet deep. Build a tiled roof over the gate so that no rainwater can flow into the passage. The officer in charge of blocking the sally-gate uses a pair of cart-wheels, binds them together with timber, and plasters mud over them; he fastens this device inside the sally-gate, measuring it to the width of the gateway, and has it set four or five feet inside the passage. Install the kiln-stoves and place a bellows (tuo) beside the gate; stuff the stove with concealed firewood and mugwort (chai-ai). When the enemy comes in, let the wheels down to block him, then work the bellows to smoke him out.