Seven metres across and sunk a metre and a half into the ground, it was not a drain or a boundary ditch but the working infrastructure of a medieval mill, quietly preserved under centuries of urban accumulation until excavations in 1995 brought it back into view.

The site at 30 to 32 South Earl Street sits within what was once the Medieval Liberty of St Thomas, a jurisdiction associated with the medieval Abbey of St Thomas. These liberties were semi-autonomous administrative territories granted to religious houses, giving them considerable control over the land and its use, including the right to operate mills. The pottery recovered from the channel dates to the thirteenth and fourteenth centuries, and the structure may well be the physical remains of a mill referred to in documentary sources as the 'Watte mill', recorded in 1272. If that identification is correct, it places milling activity on this site in the early decades of Anglo-Norman Dublin, when the abbey and its surrounding lands were being actively developed. The association was proposed by Hayden in a 1996 report on the excavation, and while it remains tentative, the scale of the water channel does suggest a substantial, purpose-built feature rather than something incidental.

South Earl Street today is an unremarkable stretch of the Liberties, the area of inner-city Dublin that takes its name from exactly these kinds of medieval jurisdictions. There is nothing above ground to mark the site, and the excavation findings will not be visible to anyone walking past. The interest here is less in what can be seen than in what the ground once held: a functioning mill fed by a managed water channel, operating within the orbit of a monastic house that no longer exists above the surface of the city. Those curious about the wider context might visit the nearby area around Thomas Street, where some traces of the abbey's footprint are occasionally referenced in local heritage materials, though the mill site itself remains entirely subterranean.