The monument consists of a length of military road approximately 1km long, running between Connachie Burn in the S and Culachy House in the N, part of the road built between Dalwhinnie and Fort Augustus in 1731 under the direction of General Wade.
By 1730, the military roads from Dunkeld to Inverness and along the Great Glen were complete, and in order to link Fort Augustus directly to the first of these, a road was planned, running partly along the upper Spey valley and climbing to 800m at the Corrieyairack Pass to cross the watershed. The new road was 45km long; work was started in April 1731 and completed by the end of that October, at a cost of L3281 4s 9d. Some 17.5km of this road remains unmetalled.
The intention was to construct the road of layers of rammed stones, with large stones at the bottom, topped by smaller ones, to a depth of over a metre. In stretches with firm subsoil, however, this is likely to have been reduced. In places can be seen patches of flat stone cobbles, which may be remains of the original surface, but for much of its length the road is likely to have been surfaced with gravel. Wherever the terrain allowed the road was flanked by a ditch on the uphill side (and in parts on the downhill side) and a further uphill ditch appears in some places, either parallel to or in place of the roadside ditch, approximately 8m from the edge of the road.
The road was abandoned north of Laggan in 1830, and thereafter the route reverted to its former use as a drove road.
The area to be scheduled measures 30m wide, centred on the road bed of the military road, running between Connachie Burn and a point 450m SW of Culachy House, as marked in red on the accompanying map, but excludes the modern structure of the bridge over the Connachie Burn. It includes the road, its associated ditches, and an area which may contain evidence for their construction and use.