The Drop Redoubt was a key element of the Western Heights fortifications. Occupying the eastern end of the ridge and dominating the town, port and seaward approaches, it is essentially a pentagonal fort designed to control the land front as a self-defensible work but was also linked to the linear defences that guarded the Heights as a whole. The 1840's and 1850's saw renewed concerns about the re-emergence of French power and significant developments in weapons technology resulted in a re-appraisal of the nation’s defences. One of the most major additions to the Drop Redoubt fort which was a result of this re-appraisal comprised two-storey caponiers at four corners of the redoubt, for defence of the ditch itself. This also enabled new casemated gun rooms to be built behind the curtain wall, reached via the caponiers, to provide flanking fire along the ditches of the North Lines and the North-East Line. The principal function of the caponiers was to flank the ditch of the redoubt with both carronade and musketry fire to prevent an attacker gaining a lodgement next to the curtain wall or attempting to scale or mine it. (location accurate to the nearest 1m based on available information)