in fortification, or **Portern-Gates**, as they are sometimes called, are those under-ground passageways which lead from the inner works to the outward ones; such as from the higher flank to the lower, or to the tenailles, or the communication from the middle of the curtain to the ravelin. When they are made for men to go through only, they are made with steps at the entrance and going out. They are about 6 feet wide and 8½ feet high. There is also a gutter or flume made under the sally-ports, which are in the middle of the curtains, for the water which runs down the streets to pass into the ditch; but this can only be done when they are wet ditches. When sally-ports serve to carry guns through them for the out-works, instead of making them with steps, they must have a gradual slope, and be 8 feet wide.