Devenish, an island in Lough Erne, Co. Fermanagh, is one of the greater Irish ecclesiastical sites (McKenna 1931; Radford 1970) and is considered to be the most important of Lough Erne's many island church settlements. The ruins are in state care. The church site was founded in the 6th century AD and functioned until the early 17th century [burial practice continuing into the 19th century]. It was raided by Vikings in AD 837 and burned in AD 1157, but in the middle ages flourished as the site of a parish church and St Mary's Augustinian Priory. The site was also a likely stop over for waterborne medieval pilgrims en route to St. Patrick's Purgatory in Lough Derg in county Donegal.
Fig.1 3D LiDAR DTM of Devenish Island
 Past Work
There has been considerable work carried out at the site from the 1960s and 1970s onwards in terms of excavation and survey (see for example, Waterman 1979; Hamlin & Lynn 1988; Hamlin & Stalley 2002). In addition between 1999 and 2002 researchers at the CMA carried out an extensive underwater geophysical survey of Lower Lough Erne (Laffery & Quinn 2003; Lafferty et al. 2005). One distinct cluster of 22 anomalies was identified in the channel between the western shore of the Island and the mainland. This area corresponds with the western ferry crossing and a great many of these anomalies are thought to be boats of various kinds lost or even discarded over the years. It was certainly not unknown for funerary boats to be lost especially if the '...mourners had partaken of strong refreshment' and such an event is recorded in 1824 when a large 'cot' overturned whilst making the crossing in bad weather (Trimble 1919). In addition an inferred causeway was also identified on the eastern side of the island which enforces a tradition surviving into the 19th century '...that Devenish was anciently connected with the mainland by a tochar or causeway...' with 'rude piers' extending '...a considerable distance into the waterâ€¦' (Wakeman 1874).
Fig. 2 Devenish Island underwater anomaly (No. 10) imaged at 100kHz in June 2000 – a sub-linear shaped feature c. 14m x 2m (hardcopy image from Lafferty & Quinn 2003). Note new digitial underwater survey imagery will allow for data integration in a GIS.
More recently the Northern Ireland Environment Agency [NIEA], Built Heritage commissioned a high resolution LiDAR survey at a target resolution of 60 points per m² [a notional ground spacing of 12.5cm] of the island. The LiDAR visualizations have vastly improved upon existing earthwork surveys carried out in the past by the heritage agency and provide new insights into the medieval monastic landscape surrounding the central church complex.
 New Insights
One such new insight is the imaging of a 'hollow-way' or path that leads away from the church complex to what would have been the western ferry terminal. This ferry crossing was used up until the 19th century by funerary parties. An antiquarian writing in the 1800s described it as thus, '...a very rudely constructed tochar or path…, leads to a port…, situated on the western side of the island…. It is composed almost entirely of small rough surface-stones, and is the only road by which funeral processions from the main land proceed to the cemeteries' (Wakeman 1874). The LiDAR Local Relief Model [LRM] clearly images this pathway and its terminus at the former pre-drainage shoreline – the site of a potential medieval landing place or "port'.
Fig.3 3D LiDAR Local Relief Model [LRM] draped over orthophoto. Note position of relict ferry terminal (highlighted in red) and underwater geophysical anomalies [yellow boxes]
 Present Work
This potential 'bridging' location, "port' and the channel between the island and the mainland are the focus of a current research project being undertaken at the Centre for Maritime Archaeology [CMA]. This work builds on the work of Lafferty et al. (2005) utilizing shallow water side-imaging sonar in conjunction with dive-truthing. The new airborne LiDAR and conventional aerial photography are also being used to better contextualize these crossing points as part of a wider monastic landscape
Fig. 4 3D Bathymetric capture at western ferry terminal
In May 2012 a preliminary underwater sonar survey was conducted. From the data collected it has been possible to recreate a picture of the underwater terrain and identify and mark anomalous features imaged on the bottom. These potential targets have been mapped in a GIS and will inform a higher resolution second-phase survey scheduled for later in 2012 and a programme of diving at the site.
Fig. 5 Example sonar imagery from May 2012 underwater survey
The author is grateful to Built Heritage [Northern Ireland Environment Agency] for having provided the LiDAR data.
[with full acknowledgement to C. Foley2 and J. O'Keefe2 for LiDAR data supply]
Hamlin, A. and Lynn, C. (eds), 1988. Pieces of the Past. Belfast.
Hamlin, A. and Stalley, R. 2002. "A Newly-Discovered Romanesque Church on Devenish, County Fermanagh'. Ulster Journal of Archaeology, Vol. 61, 83-97.
Lafferty, B. and Quinn, R. 2003. Report on a Geophysical Survey of Lower Lough Erne. Report No: CMA GR 001. Prepared for: Environment and Heritage Service, Department of the Environment for Northern Ireland.
Lafferty, B., Quinn, R., Breen, C. 2005. "A side-scan sonar and high-resolution Chirp sub-bottom profile study of the natural and anthropogenic sedimentary record of Lower Lough Erne, northwestern Ireland'. Journal of Archaeological Science 33, 756-766
McKenna, J.E. 1931. Devenish (Lough Erne): Its History, Antiquities, and Traditions. Dublin/Enniskillen.
Radford, C. A. R. 1970. 'Devenish', Ulster Journal of Archaeology, Vol. 33, 60.
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Wakeman, W.F. 1874. "The Antiquities of Devenish'. Journal of the Royal Historical and Archaeological Association of Ireland, Vol. 3, No. 17, 59-94.
Waterman, D. M., Pearson, G.W., Griffith, A.E., and Wilson, R.A. 1979. 'St Mary's Priory, Devenish: excavation of the east range, 1972-4'. Â Ulster Journal of Archaeology, Vol. 42, 34-50.