A tactical outpost used by soldiers to protect the frontier of the Roman Empire has been discovered in central Scotland.

The remains of a Roman fortlet which stood next to the Antonine Wall in central Scotland has been uncovered by archaeologists using ground penetrating technology.

The miniature fortification, which would probably have housed a handful of legionnaires standing guard along the front line of the Roman Empire, was thought to have been lost in the mists of time.

The existence of the 1,800-year-old historic structure was only known because of a reference made to it more than 300 years ago. Antiquarian Robert Sibbald wrote in 1707 that he had seen a fortlet in the area around Carleith Farm. Despite several attempts by various excavation teams in the 1970s and 1980s no real trace could be found and the exact location remained unknown.

However, a geophysical survey in an unassuming field near Carleith Primary School in West Dunbartonshire has at last revealed details of the buried remains that have been lost for centuries.

The team of archaeologists used 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 two metres high.

It is believed the fortlet would have been part of several such structures along the Antonine Wall which would have been occupied by 10 to 12 Roman soldiers. Historians think they were probably stationed at a larger fort nearby, likely to be Duntocher, and manned the outpost 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 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.

“It is great to see how our knowledge of history is growing as new methods give us fresh insights in the past,” said Riona McMorrow, Deputy Head of World Heritage at Historic Environment Scotland (HES).

“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.”

The discovery has led to HES reviewing the site’s designation to ensure the fortlet is recognised and protected as part of 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 10th and shows that there is still more to be discovered about this important Roman monument and its functions even after centuries of enquiry.