This was a device of classical fortification designed to enhance the depth of the ditch by artificially increasing the height of the outer (northern) face of the ditch using spoil from the excavations. The southern part, effectively an extension of that outer face, was the glacis. The northern slope was the counterscarp. The terminology (which derives from Renaissance fortification techniques) sometimes gets a little confused when applied to the Wall ditch (it is sometimes referred to as an ‘upcast mound’) but there is no doubting its function: to enhance the outer lip of the ditch. It only survives intermittently along the northern edge of the ditch and it may not have been continuous.