Bridge, Clonmacnoise, Co. Offaly

It was first noticed in 1994, when a preliminary underwater survey picked out a cluster of wooden posts and beams on the riverbed. Further survey work in 1995 suggested these were no random scatter but the remains of a coherent structure, with around 100 timbers surviving, among them vertically set posts, longitudinal and transverse beams, and planking joined with a level of carpentry that only became clearer on closer inspection.

Dendrochronology, the technique of dating timber by its annual growth rings, placed one post from the northern side of the bridge at AD 804, which aligns the structure with the height of Clonmacnoise's influence as a monastic and trading centre on the Shannon. Excavations led by Aidan O'Sullivan, Niall Brady, and Donal Boland between 1997 and 1998 established that the bridge had spanned the full width of the river without interruption, its posts sharpened and fitted through mortised joints into individual base-plates, a sophisticated construction for any period. Among the objects recovered from the riverbed were eleven dug-out boats, four early medieval iron woodworking axes, a decorated bronze basin, iron slag, and a Mesolithic chert core, the last a reminder that this crossing point had been significant long before the monastery. One of the boats recovered upstream of the bridge was at least 7.75 metres long with a flat bottom and slightly raised ends, resembling the river cots shown on early modern maps of Ireland, and was the largest example found across the entire project.

The excavators noted with some concern that the bridge timbers, lying only a short distance below the waterline, are vulnerable to the erosion caused by boat traffic on the Shannon as well as the natural movement of the river. The eleven dug-out boats were lifted, drawn at scale, photographed, and returned to a known location downstream for safekeeping, with conservation of at least some of them planned for the future. A scatter of timbers found 100 metres downstream, initially thought to be remnants of the original superstructure, turned out on investigation to be the decayed posts of a modern barbed-wire fence running from the Anglo-Norman castle to the riverbank, a cautionary reminder that not every promising timber on the riverbed has a medieval story to tell.