Birrens: putting a Roman fort in context

We had a great week of survey at Birrens Roman Fort, near Middlebie, earlier in the

Tom and Ron carrying out resistivity survey

month. Overall, volunteers, together with University of Glasgow students and staff walked nearly 35km, collecting some fascinating data that has really helped to put the Roman fort into context.

We had a number of visits from the local media. Giles Carey and Dr. Richard Jones explain here a bit of background to the fort and what the survey hoped to achieve.


Courtesy DNG Media

And the results were definitely worth braving the weather for. Dr. Richard Jones, who led the work, is excited by the results. He said:

The results of this survey at Birrens are exciting because they seem to show a fort lying next to, and probably earlier than, the known (excavated)  fort.  As well as the defences, there is a lot of  detail within this new fort which we want to understand.

Whilst the results will undergo further analysis and interpretation, a number of features are already apparent.

To the west of the fort
A large scale magnetic survey was conducted to the West of the earthworks of the fort, where a series of ramparts and the line of the Roman road are visible on aerial photographs. This field is currently under pasture, and gives little indication of what lies beneath.

Magnetic survey gets underway – little survives above ground

However, the results are quite staggering. Below is a greyscale view of the results. The readings taken as the equipment is walked across the ground surface are all plotted together, and have been placed on a map to reveal a buried ‘plan’ of archaeological deposits. Areas of positive magnetic response are shown as black; areas of negative magnetic response are shown as white. These results show a series of features which correspond well with the aerial photographs of the site.

Initial results of magnetic survey to West of fort.

A series of buildings are visible, aligned along north-south and east-west streets, within a fort with considerable ramparts to the North and West. A number of other features can be suggested – a line of circular anomalies close to the intersection of the roads could be a series of ovens. What is clear is that there was a sequence of rebuilding here, and what survives today is only a small part of a much more extensive military landscape in use over at least 100 years.

Initial interpretation: yellow: road, purple: defences; green: weak features to the west of the fort/annexe; light blue: narrow positive magnetic anomaly running from the fort interior approximately westward into the annexe.

Volunteers also carried out some resistivity survey in this western annexe – and the roads are immediately obvious in this data.

To the north of the fort
A resistivity survey was carried out to the north of the surviving fort earthworks, covering 22 grids in an area which aerial photographs suggested the via principia  (the main road) of the fort might run through.

The results are a bit harder to interpret, but there are certainly features here which are suggestive of large ditches. It is likely that we will be returning to carry out some more magnetic survey in this area – it might help us clear up exactly what is going in this northern area.

The resistivity survey detects changes in the moisture level of the soil related to archaeological deposits below the ground. The greyscale below shows initial interpretation – the white areas indicate areas of low resistance. Here electrical current passes through the soil more easily, indicating that buried deposits are damper – such as might be found in a ditch. The black areas indicate high resistance. These might indicate buried stonework – electrical current cannot pass so easily through the soil around a wall for instance, because it is drier.

Initial interpretation of resistivity survey. Yellow: drains; red: low resistivity anomalies some of which may represent ditches; blue: higher resistivity anomalies of uncertain identity.

Overall, this data has really helped to show that there’s more to Roman activity in this area than meets the eye. A lot is buried below ground, that we just can’t see any more above the surface. The results of the geophysical survey are very important therefore in finding out more about this complex military landscape.

A huge thank you to all our volunteers – who braved some challenging weather and sheep! We would also like to say thanks to the 50 or so people who turned up to see the results on the Open Day – it was a very enjoyable day.  

The small display receives its first Open Day visitor

We would also like to thank Middlebie Parish History Group for their support, particularly Janet Foreman and Ian Aitken-Kemp, and to our project funders as well as to the Mouswald Trust and the Dumfries & Galloway Natural History and Antiquarian Society and the landowner, Mr Denis Martindale.

A tired but happy team

Would you like to be part of the volunteer team next time? Please contact us to find out about upcoming surveys.

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