But the low earthwork that defines this particular field, a scarp some forty metres north to south and thirty-eight metres east to west, with what appears to have been a water-filled moat around it, may mark the site of a medieval mill that once served an entire local economy. Or it may not. That uncertainty is itself part of what makes the site worth knowing about.

The earliest documentary reference comes from the Civil Survey of 1654 to 1656, which recorded that Sir Moris Hurly of Cnocklong, described in the survey's blunt language as an Irish Papist, held possession of a ruined castle, a mill, two fairs, a Court Leet, and a Court Baron. A Court Leet and Court Baron were manorial courts, the local legal machinery through which a landlord administered justice and collected dues, which tells us something about the scale of Hurly's operation at Knocklong even in its declining years. The mill itself was already in a ruined state by the time the surveyors arrived in the 1650s, suggesting it had been working in earlier centuries. The earthwork sits 130 metres north-east of O'Hurley's Castle, in poorly drained ground that also lies close to Knocklong Church, its associated graveyard, and two holy wells dedicated to St. Patrick and St. Paul, all within two hundred metres. Whether the square moated enclosure was genuinely built to house and protect a mill, or whether it was shaped instead by later land reclamation works in the boggy field, remains an open question for archaeologists. No version of the Ordnance Survey six-inch maps ever recorded a monument at this location, which is part of why it slipped from notice for so long.

The site is most clearly visible not from the ground but from aerial photography, where the outline of the earthwork shows up on Digital Globe imagery. A leat, meaning a man-made channel cut to direct water to or from a mill, intersects the south-east corner, and a field drainage ditch cuts across the north-west angle, both of which hint at the water management that would have been central to any mill operation here. Visiting the area around Knocklong, it is worth being aware that the ground is genuinely wet and poorly drained, and that the earthwork reads better as a subtle change in relief than as any kind of dramatic feature. The companion sites, the castle ruin and the holy wells to the south, give useful orientation and help situate this quiet, ambiguous enclosure within what was evidently a well-organised medieval landscape.