What remains is the outline of a coastal promontory fort, a type of enclosure in which a headland or coastal projection was defended not by encircling the entire area but by fortifying only the landward neck, the narrow strip connecting the promontory to the mainland. Here, that neck was once secured by two earthen banks with a fosse between them, a fosse being simply a ditch, typically dug to reinforce the obstacle presented by the banks on either side.

The antiquarian Thomas Johnson Westropp recorded the site in 1914, noting the twin banks and the intervening ditch at the neck of the promontory. Westropp was a prolific documenter of Irish earthworks and forts in the late nineteenth and early twentieth centuries, and his field observations remain a primary point of reference for many sites along the southern and western coasts. At Rochestown, his account has proved quietly accurate in one particular respect: the site has changed very little since he visited, not because it has been preserved or managed, but simply because the sea erosion that was already eating at it in his time has continued at much the same pace, leaving the surviving earthworks in roughly the condition he described.