But this modest causeway, running for about 150 metres just north of Brandane church, is all that remains of a medieval tide mill, a type of mill that used the regular rise and fall of the sea rather than a river current to drive its machinery. A millpond would be filled at high tide, then the water released in a controlled flow to turn the millwheel as the tide dropped. The causeway itself, stone-cored and no more than a metre or two wide, served as the dam that made this possible.

The mill at Bannow appears in records as early as 1307, making it one of the earlier documented mills in the region. By 1324 it was already described as ruinous, which suggests either hard use or straightforward neglect, and perhaps both. It passed through various hands over the following centuries, and by 1634 it formed part of the estate of John Cullen of Cullenstown Castle. The causeway came to be known locally as the Black Bridge, a name that acquired some explanation around 1800 when large pieces of blackened oak were recovered from it, almost certainly the charred or waterlogged remains of the millhouse itself. That detail, a mill quietly dissolving into its own foundations over centuries, was noted by Tuomy in 1850. The identification of the site as a tidal mill, rather than a conventional watermill, was made more recently, drawing on the physical evidence of the causeway and the tidal geography of the inlet.

The causeway still crosses the inlet, a low grassy bank with a gap of around 15 metres near its southern end. That break may have been where the sluice or millrace once sat, the functional heart of the whole operation. The church at Brandane provides the clearest landmark for finding it.