Unlike the more familiar vertical waterwheel, the horizontal mill, sometimes called a tide mill or click mill depending on its configuration, used a wheel laid flat beneath the millhouse floor, turned directly by a jet of water channelled through a wooden or stone trough. This simpler mechanism required no gearing to transfer power to the millstone above, making it cheaper to build and easier to maintain, which is precisely why it spread so widely across early medieval Ireland and persisted in marginal landscapes long after more elaborate mills had taken over elsewhere.

Horizontal mills appear in Irish annals and law texts from at least the seventh century, and archaeological evidence suggests they were a cornerstone of local grain processing for rural communities throughout the medieval period and beyond. The townland name Boherduff, from the Irish Bóthar Dubh meaning the black road, hints at an older landscape of paths and use, the kind of place where a small mill serving a cluster of farms would have made quiet, practical sense beside whatever watercourse once powered it. These structures rarely announced themselves; they were working buildings, modest in scale, built from local stone and timber, and they tended to be positioned wherever a stream could be persuaded to deliver enough force through a narrow flume.