The Fortlet was built next to the Antonine Wall, the frontier that the Romans constructed across central Scotland, and was thought lost in the mists of time. However, geophysical survey in an unassuming field near Carleith Primary School in West Dunbartonshire revealed details lost for hundreds of years.

Previous excavations to find the fortlet were unsuccessful, but new technology has allowed HES’s archaeological survey team to find the buried remains. The fortlet was referenced in 1707 by antiquarian Robert Sibbald, who wrote that he had seen a fortlet in the area around Carleith Farm. Excavation teams looked for it in the 1970s and 1980s, but the exact location remained unknown.

The survey team have now employed gradiometry, a geophysical surveying technique, to look under the soil without the need for excavation. Gradiometry measures small changes in the earth’s magnetic field to detect archaeological features otherwise invisible from the ground surface. This technique was able to identify the stone base of the fortlet, which remains buried underground. On top of this base, turf would have been laid to build a rampart about 2 metres high.

This newly discovered fortlet would have been part of several fortlets along the Antonine Wall. It would have been occupied by 10 to 12 Roman soldiers who were stationed at a larger fort nearby, likely to be Duntocher, and manned the fort for a week at a time before being replaced by another detachment. The fortlet would have been made up of two small wooden buildings to house the soldiers staying there and will have been used for the 20 years (142 CE – 162 CE) that the Antonine Wall was defended as the northernmost frontier of the Roman Empire.

Commenting on the discovery, Riona McMorrow, deputy head of world heritage at HES, said: “It is great to see how our knowledge of history is growing as new methods give us fresh insights in the past.

“Archaeology is often partly detective work, and the discovery at Carleith is a nice example of how an observation made 300 years ago and new technology can come together to add to our understanding.”

This discovery has led to HES reviewing the site’s designation to ensure the fortlet is recognised and protected as part of the Antonine Wall.

The geophysical survey will help to better understand and protect the Antonine Wall. While up to 41 fortlets may have lined the Wall when it was built, only nine have previously been found. This discovery marks the tenth known fortlet and shows that there is still more to be discovered about this important Roman monument and its functions even after centuries of enquiry.