When construction crews began work on the Four Courts extension in Dublin in 1984, they uncovered something that had been sealed underground for the better part of seven centuries: a stone-lined channel complete with a timber sluice-gate, a piece of infrastructure that once directed water through what is now the north city's legal quarter.

Excavations that year revealed the channel running on a northwest to southeast alignment over a length of thirteen metres. It was built in the drystone tradition, meaning the stonework was laid without mortar, and measured roughly three quarters of a metre wide. The floor was flagged, and the side walls, standing to about 0.77 metres in height, were faced on their inner surfaces with roughly dressed limestone blocks. A sluice-gate is essentially a sliding panel or barrier used to control the flow of water through a channel, and the survival of the timber components here was significant. Dendrochronology, the science of dating wood by analysing its annual growth rings, placed the construction of the channel in the mid to late thirteenth century, a period when Anglo-Norman Dublin was expanding rapidly and the management of water for mills, drainage, and domestic use was a practical necessity of urban life. The findings were published by McMahon in 1988, providing the primary record for this structure.

There is nothing to see at ground level today. The channel lies beneath the Four Courts complex on Inns Quay, and access to the site itself is not possible for casual visitors. The value of this place is perhaps best appreciated through the published record rather than a physical visit, though standing on the quayside and considering what lies a few metres underfoot does offer a particular kind of perspective on how layered Dublin's ground actually is. Anyone with a serious interest in the medieval archaeology of the city would find McMahon's 1988 report, cited in the excavation records, a worthwhile starting point for understanding the extent of what was uncovered here.