Bridge in Coolumber

The bridge of Curr Clwana was built by 1158 connecting the castle of Clonmacnoise, Co. Offaly (OF005-003001-) with Connaught (AClon.). The site of an earlier ninth-century wooden bridge was first discovered in 1994 by two local divers (Donal Boland and Mattie Grehan).  The bridge crossing the River Shannon was surveyed in 1994-5 by members of Irish Underwater Archaeological Research Team under the archaeological direction of Colin Breen and Aidan O'Sullivan when 123 timbers were located (Byrne and Mass 1995). The ninth century wooden bridge, connected the Slí Mhór (Great Road) of Clonmacnoise monastery on the eastern side of the River Shannon with a gravel road in Coolumber bog (RO055-005----) in Co. Roscommon, on the western side of the Shannon.  The structure was approximately 120m long by 4-5m wide with oak posts standing c. 6m high above the river bed.  The bridge consisted of rectangular frames supported on 25 pairs of vertical posts placed c. 5m apart, 17 pairs of oak posts were identified by the excavators. Dendrochronological dates of 786 and 804 were recovered from two timbers. Six log boats were also located (Moore 1996). No trace of the bridge mentioned in 1158 has been identified in this area.   It has been suggested by the excavators that the bridge had a lifespan of 40 or 50 years after it was constructed. Cross reference with OF005-065----.  Underwater archaeological excavations were carried out by Aidan O'Sullivan, Niall Brady and Donal Boland under licence no. 97E0243 over a four-week period in June 1998 on an early medieval wooden bridge crossing the River Shannon at Clonmacnoise. The excavations were funded by the NMHPS. The bridge lies between Clonmacnoise townland, Co. Offaly, and Coolumber, Co. Roscommon, crossing a narrow part of the river west of the Anglo-Norman masonry castle. Previous work on this site included both underwater survey and excavation.  In 1994 a preliminary underwater survey in the River Shannon at Clonmacnoise identified a number of wooden posts and beams on the riverbed. A more detailed survey carried out in 1995 seemed to indicate that the timbers were the remains of a bridge, from which some 100 timbers seemed to survive. These included vertically set posts, longitudinal and transverse beams, planking, and complex carpentry. A dendrochronological sample from a post on the northern side of the structure yielded a date of AD 804. A series of dug-out canoes was also revealed, lying on the riverbed and among the structural timbers. Underwater archaeological excavations in 1997 (Excavations 1997, 148-9) investigated the nature of the bridge's construction. This revealed that the structure was built using a complex method of sharpened and through-mortised posts with individual base-plates of beams and planks. There were also hints of the superstructure of the bridge in the occasional well-preserved vertical timber now lying on the riverbed.  Finds from the survey and excavations included nine dug-out wooden boats; four early medieval, iron, woodworking axes; a large, early medieval, decorated bronze basin; iron slag; a whetstone; animal bone; and a Mesolithic chert core. These excavations also confirmed that the bridge spanned the river from bank to bank and that it was uninterrupted in its length. In 1998 a third season of underwater investigations at Clonmacnoise was carried out. The project aimed to answer a number of unresolved questions about the preservation of the dug-out canoes, the status of a previously identified timber scatter lying downstream and the nature of the archaeology upstream of the bridge, which had hitherto been unexplored.  The first aim of the project was to lift, record and assess the erosion of the dug-out boats. There were concerns that those on the riverbed were the most subject to erosion of all the features, all of them having lost ends and sides to the constant erosion of the channel and the movement of mussel shell fragments. It was decided to lift and record these boats and move them to a safer location. Therefore, in the first two weeks of the excavations each boat was lifted and brought up to the riverbank. This task was accomplished using buoys and lifting slings.  The boats were then drawn at 1:10 scale, with cross-sections and profiles completed. Each boat was also photographed in detail. It was clear that more information could be gleaned from the boat in the open air than underwater. At the close of the season each boat was transported back into the water and left at a known location downstream of the bridge. It is intended that some, if not all, of these boats will be fully conserved in the future. The second aim of the project was to assess the archaeology of a scatter of timbers found 100m downstream of the bridge adjacent to the east bank. These timbers had been surveyed in detail during the 1995 season, so it was possible to return to their location. However, it had not been possible to record them any more closely during that survey season, as they were lightly buried in the river silts.  It was suspected that they were the remains of the original early medieval bridge's superstructure and that they could therefore supply much useful information on the carpentry of bridge. However, during the 1998 season, after rapid exposure on the riverbed and timber recording, it became evident that all of these downstream scatter timbers were modern in origin. They were all of pine roundwood, sharpened at one end and heavily rotten from exposure to wetting and drying. These posts probably derived from the riverine end of a modern barbed-wire fence that runs down to the river from the west side of the Anglo-Norman castle. They therefore have no relationship of any kind with the early medieval bridge. Indeed, it now seems likely that little or no trace of the original bridge superstructure remains in the river. A third aim of the project was to extend the underwater survey upstream of the bridge, bringing the investigated area up to the riverbank of the monastic site. A survey was carried out along the east bank, to a point 200m upstream of the bridge and out to the middle of the river channel. There was no evidence of any wooden structures in this area. A number of finds were made, including wooden objects, iron buckets and various other objects. Most importantly, the remains of two more dug-out boats were found on the riverbed. One example was unusual in that it had a flat bottom, with slightly raised ends, in the manner of river cots depicted on early modern maps of Ireland. This boat is at least 7.75m long and is the largest yet found.  A remote-sensing survey of the riverbed was also carried out by Kevin Barton of the Geophysics Department, UCG, using differential GPS and a bathymetric sonar survey. The present programme of underwater archaeological investigations of the early medieval bridge at Clonmacnoise can now be considered complete.  The project has been high successful, accomplishing in a relatively brief period the detailed recording of a substantial 9th-century wooden bridge and the recovery and curation of eleven dug-out boats and various metalwork finds. However, there are serious concerns about the future preservation of this unique structure, as this stretch of the River Shannon is subject to an ever-increasing volume of boat traffic and large cruisers. This, as well as natural riverine erosion, may well be having a detrimental effect on the archaeology that lies only a few metres under the water. Compiled by: Michael Moore and Caimin O'Brien Date of upload: 24 August 2010