Monument record MHG55804 - Early C19 bridge - Allt Lagain Bhain, Dundreggan, Glenmoriston

A now disused bridge over the Allt Lagain Bhain near Dundreggan, Glenmoriston, dating to the early C19 and probably built under instruction from Thomas Telford was subject to desk-based assessment and a condition survey in 2012 by CFA Archaeology prior to proposed demolition.

It is a single arch bridge and comprises two spandrels either side of a segmental arch. The deck measures c.12m long by 5m wide and is surfaced with pioneer grass covering the remains of a rough metalled gravel surface. The west end of the bridge merges into the surrounding landscape and the east end merges into the road verge. The bridge is built around a 4.7m wide and 1.6m high segmental arch set on 0.6m high abutments set into the banks . The arch is constructed from granite voussoirs and both abutments are built from basalt blocks. At the time of the survey the abutments were not clearly visible due to being both overgrown and hidden by gravels and stones washed down by the stream. The arch soffit was thickly lime rendered. It was judged to be in poor overall condition.

Cartographic sources suggest a construction date for the A887 between the late C18 and the beginning of the C19. It seems likely that while a built route was in place from 1784 it was developed into a more vital conduit towards the end of the first decade of the 1800s and recognised as such by cartographers. The completion of the nearby Torgyle Bridge by Thomas Telford in 1811, thus improving access from Invermoriston to the west, supports a hypothesis that the road began as a minor local track and developed into a main road around this time.

The inconsistent depiction of the road (now the A887) carried by the bridge on historic maps both before and after its likely construction date suggests that it evolved as a minor road used primarily by local traffic rather than it being built from the beginning as a main artery; the military road from Fort Augustus appears to remain in use during this time and would have presented a more direct route from the larger centre of Fort Augustus to the north-west, albeit via a more elevated route which would be more exposed to weather, especially during winter.

It was subsequently replaced by a new bridge, built probably sometime in the early C20 (see MHG55805). <1>

A Level 3 building survey was carried out by CFA archaeology in January 2013 prior to the demolishment of the bridge in order to install a box culvert. <2>