Monument record MHG34943 - ALLT THOMAIS BURN BRIDGE

A mid-late C18 single arch bridge spanning the Allt Thomais Burn near Achlain on a stretch of the military road between Fort Augustus and Fort William.

This bridge over the Allt Thomais Burn is of military construction, 4.5m wide and with a span of 2.5m. The arch ring is complete, although upper stonework is starting to disintegrate.
Visited by OS April 1979.

The bridge was visited by M Logie of Historic Scotland in 1997 during a project involving a rapid assessment of the state of the military roads and associated features within the boundaries of the Highland Council area. This bridge was noted as being a single span stone culvert/bridge, 2.5m wide with arch ring complete and its upper stone work beginning to disintegrate. <1>

The bridge was included in a survey in 2009 by Forestry Commission Scotland of C18 military roads under their ownership within their Highlands estate and within the districts of Inverness, Ross and Skye, Lochaber and the North Highland Forest in order to enable it to develop sustainable management strategies. <2>

AOC Archaeology Group was commissioned by Forestry Commission Scotland in 2011 to undertake a Structural Costed Conservation Plan for the Achlain Bridges, Fort Augustus, in line with their aspirations to conserve the bridges as a heritage asset through repair and maintenance as necessary. The three bridges date to the mid-C18 and form part of the military road constructed between Fort Augustus and Bernera by Major Caulfeild, the successor to General Wade, in response to the Jacobite uprisings. The plan incorporated an assessment of the significance of the bridges, an assessment of its current condition and conservation requirements and the identification of the long-term needs to maintain them. Archaeological recording of the bridge (designated bridge 007) included a detailed measured survey, a 3D Laser scan, a general and detailed photographic record and a detailed written record. Bridge 007 is the smallest and easternmost of the bridges and is constructed of sandstone with stone slate pinnings and forms a single segmental arch with low abutment walls of three courses in depth. On initial inspection, the bridges look almost to be of drystone construction, although closer inspection identifies that the build was lime mortared, the majority of which has been washed out by general erosion. <3>

Ross and Cromarty Archaeological Services were commissioned by Forestry Commission Scotland to undertake a programme of recording and excavation in advance of conservation of three military bridges located by Achlain in Invermoriston during the second half of 2012. A single small trench was excavated at the centre of the arch on Bridge 007, prior to conservation. The excavation allowed for recording of the bridge prior to any changes made by conservation work to the structures. <4>