The North Gateway or Northern Entrance to the Western Heights defence complex was first planned during the Napoleonic Wars but they were only partially completed. Between 1858 and 1867, partially as a result of the Royal Commission on the Defence of the United Kingdom in 1859, the defences around the Western Heights were completed. By 1870 the North Gateway mounted two 18-pdr SB carronades, possibly upgraded to 24-pdr carronades. Loop holes were provided for rifle fire.
The North Gateway included a tunnel, running from Drop Redoubt Road, out to the two bridges across the Norther Lines Moat. Casemated scarp positions provided flanking fire along the dry moat of the Norther Lines.