The drawing referred to shows the Old Mole detached and joined only by a timber bridge to the said counterguard, with the works completed by 1804. Furthermore, part of a tenaille [a small outwork placed to cover the curtain between two bastions] has been built in front of the curtain between the North and Montagu Bastions and the shape of the ravelin in front has been altered. A ravelin was an outwork placed beyond the ditch and having two faces and a gorge and usually provided with flanks; thus, it looked like a detached bastion. In 1859 it had sixteen guns. On its north-western outer face, there is still evidence in the present day of a blocked-up postern gate, previously a sally port, which served as an early link, via a footbridge, to the Devil’s Tongue Battery.
Montagu Counterguard was the second in an envelope of three counterguards, joined by thin curtain walls, the others being North-West (incorrectly named West Place of Arms) and Chatham Counterguards, that protected North Bastion, Montagu Bastion and Orange Bastion respectively.