When an environmental impact study was carried out ahead of the Arcon Lead-Zinc Mine at Galmoy, Co. Kilkenny, archaeologists found something unexpected in the townland of Castletown: the remains of a small earthwork fortification, pentagonal in plan, that had been hastily built, briefly used, and then deliberately destroyed, probably all within a few years of one another in the mid-seventeenth century.

Excavation in 1999 confirmed the site as an earthen outwork redoubt, a type of detached defensive position designed to protect a larger fortification or control a particular approach. The structure was built with some knowledge of contemporary military engineering. A V-shaped fosse, or ditch, between five and five-and-a-half metres wide and up to two-and-a-half metres deep, turned through sixty degrees to create the characteristic pentagonal outline. Two demi-bastions, projecting platforms that allowed defenders to cover the walls on either side, were identified at the north and west angles. A hornwork, an outer defensive outwork projecting in front of the main entrance, protected the gateway. The main bank was built from stone, gravel, and sand, reinforced on its inner face by a timber palisade, with post-holes and stake-holes still visible in the ground. None of this, however, lasted long. The interior had been deliberately lowered, there were no occupation layers, and the fort appears to have been ended by fire and by pushing the banks into the fosse, most likely by the builders themselves rather than by an enemy: no cannon or musket balls were found. The crudeness of the hornwork and the speed implied by the construction all suggest a temporary installation. Edmund Shee forfeited the Castletown lands under Cromwell, as recorded by the historian William Carrigan in 1905, pointing to a date in the 1650s. Local tradition adds a different layer: a story that Cromwell granted Pierce MacOdo, also known as Coady, all the land visible from a single vantage point, which supposedly included Castletown.

The excavation produced a modest finds assemblage, some animal bone alongside military and domestic artefacts tentatively dated to the seventeenth or eighteenth centuries, not enough to tell a full story, but enough to confirm that this quiet corner of Kilkenny once held a small piece of the upheaval that reshaped land ownership across Ireland in the 1650s.