Dunmore hillfort, near Bochastle just west of Callander, is a well-known local landmark and nationally important monument. As part of our Archaeology project, the hillfort was recently surveyed using drone-based photogrammetry, a form of aerial survey that allows us to see sites from new perspectives and creates highly accurate 3D terrain models by “stitching” together hundreds of individual photographs. Matt Ritchie, National Environment Advisor (Historic Environment), from Forestry and Land Scotland tells us how cutting-edge technology can help us to better understand our ancient history.
The Iron Age hillfort of Dunmore above Callander is probably around 2,500 years old, give or take a few centuries. Located within the Woodland Trust’s Glen Finglas estate, the fort is set on a prominent knoll on the southern slopes of Ben Ledi (at NN 601 076). Four prominent ramparts enclose the western slopes of the knoll, with steep cliffs defending its south-eastern arc. The site has never been excavated, but it was likely the seat of a local Celtic chief.
In March 2019, Skyscape Survey carried out a drone-generated photogrammetric survey of the hillfort, combining the results with innovative visualisation techniques to produce a suite of new illustrations. Here, surveyor Hana Kdolska is preparing the DJI Inspire quadcopter drone before its flight.
To undertake an airborne photogrammetric survey, hundreds of photographs are taken of a site and processed using point-matching software to create a 3D terrain model. Height detail is then refined by adding close contours and orthographic colour. In this image, the 3D terrain model is viewed with real time colour (top) and using contours set 0.1 m apart (bottom).
See below a 3D model of the hillfort created using Agisoft Photoscan. If you click and hold your mouse while moving it to the left or the right, this model can be spun around, allowing you to view and analyse the hillfort from any angle. This adjustable 3D perspective helps us to appreciate the contours of the surrounding landscape, for example, the steep cliff-edge, which probably indicates why ramparts were only constructed along the comparatively accessible north and western sides of the hillfort.
The model can then be used to create an archaeological measured plan, accurately describing the location of the ramparts on the west of the hill and three likely roundhouse platforms. The ramparts were probably set with palisades or hurdles, while the roundhouses would have been made of timber and thatch, with low conical roofs. An annex to the main site is located down the northern slope, while the precipitous cliff-edge can clearly be seen along the south-eastern corner of the hill. The image also shows a central well and a bomb crater to the east of the summit.
The archaeological methodology was demonstrated to a group of Callander’s Landscape volunteers during a guided walk to the fort on the 19th March. The volunteers praised the “innovative” approach of this survey and one person said it helped them to obtain “an insight into the wealth of archaeology in my area”.
Find out more about our Archaeology project here.
To plan your own visit to Dunmore, please visit the Woodland Trust’s website.
The copyright of all images in this article is owned by Skyscape Survey 2019.