They came to light not through archaeological excavation but as a byproduct of land reclamation works along this stretch of the river near Cooperhill, Co. Limerick, and their discovery in 1958 was accompanied by something even more arresting: an iron sword of Viking Age manufacture, found at the same depth of sixteen feet below the surface.

The timber structure is thought to be a wooden trackway or, possibly, a boat-hard, a term for a hard-surfaced landing place where vessels could be drawn up out of the water in a tidal creek or saltmarsh. A trackway of this kind, sometimes called a tochar in Irish contexts, was typically built by laying timber across soft or waterlogged ground to create a stable surface for movement. Aidan O'Sullivan, cataloguing the site in 2001 as "Cooperhill 1", noted that the combination of the findspot description and the depth at which the materials were recovered points strongly toward a wooden structure within a saltmarsh creek environment. It has been suggested that the causeway may have served as a route toward Muckinish, lying further to the north. The Viking sword found alongside it places the site broadly within the Viking Age, though without further analysis it is impossible to be more precise about the date or the circumstances of the sword's deposition.

There is nothing to see at the surface today. The site does not appear on recent satellite imagery, and it has not been formally visited or excavated by researchers. The landscape around Cooperhill is now reclaimed agricultural ground, flat and unremarkable from the road, with the Shannon nearby but largely out of sight behind its banks and flood defences. What lies beneath belongs entirely to the archive record, specifically the National Museum of Ireland's Topographical Files, which preserve the 1958 account. For anyone drawn to the Shannon estuary's layered and largely invisible past, the interest here is less in what can be seen and more in what the combination of a sword and a row of oak trunks, buried four and a half metres down, quietly implies about who once moved through this marshy ground and why.