[1] Constructed circa 1880, the water supply cistern has a monumental entrance built into the hillside.
This cistern evidently served, inter alia, a tank slightly lower on the slope, however this is now concealed by foliage and remains inaccessible.
[1][2] At the time of construction of the citadel, the southern face of Verne Hill went through remodeling, and this was when an existing fresh water spring head was housed in the cistern's stone retaining wall, cut into the outer wall of the Verne Ditch bank, midway along and adjacent to the upper track.
[3] Before the supply of piped water to Portland in the early 20th century, this storage cistern and its works would have been an important installation.
[1][2] In recent decades the entrance of the cistern has become overgrown and inaccessible, but is often cut back and cleared.