Another Antonine Wall fortlet found

In the wake of the discovery of the Antonine Wall fortlet found at Carleith Farm in West Dunbartonshire (see CA 400), another one has been revealed, this time at Bonnyside, near Falkirk, on the more eastern side of the wall. This is now the 11th Antonine Wall fortlet to be found, out of a possible 41.

As with the Carleith Farm fortlet, this latest was discovered as part of Historic Environment Scotland’s (HES) project, ‘Seeing Beneath the Ground: a Partnership for Geophysics’, a five-year initiative funded by the Historic Scotland Foundation, which began in July 2020. By using geophysical survey techniques – including gradiometer, ground-penetrating radar, and electro-magnetic survey – the project aims to answer some of the trust’s most important research and site-management questions. It is the first multi-sited geophysical survey plan to be carried out by HES.

While HES has a list of possible areas of interest for the project, the discovery of the fortlet was rather serendipitous. The team behind ‘Seeing Beneath the Ground’ had been asked if they could be filmed carrying out a survey to be used in a documentary about the Antonine Wall (now available on YouTube:, as part of the ‘Rediscovering the Antonine Wall’ project. The Bonnyside site (Top rIGHT), situated roughly 350m west of Rough Castle (one of the 16 main forts located along the Antonine Wall, and the best-preserved), was chosen as it is one of the more ‘scenic’ locations along the wall that had not yet been surveyed.

Antonine Wall fortlets are known to have been spaced roughly every mile along the almost 40 miles of the wall, from the Forth to the Clyde. As the Bonnyside site is approximately 2 miles east of the known fortlet at Seabegs Wood and 2 miles west of another known fortlet at Watling Lodge, it was always believed that one was probably located in the vicinity of the Rough Castle fort, but as no trace of the fortlet is visible above ground, the exact location was unknown – until now.

In the course of carrying out the ‘filmable’ survey along the ridges of the Antonine Wall, it quickly became apparent that the team had chosen the precise location of the fortlet – 53m east of the position that is exactly 2 miles from the two other known fortlets mentioned above. A full survey was then carried out, revealing the northern wall in its entirely and showing that the ramparts measured 26m east to west (above). This is in keeping with other Antonine Wall fortlets, which range from between 25 and 27m across. The southern part of the fortlet, however, was truncated by an access track heading toward Rough Castle, so its north-to-south measurements could not be fully appreciated.

During the period that the Antonine Wall was defended (AD 142-162), as with all the other 41 fortlets, this one at Bonnyside would have been manned by a small, rotating contingent of 10-12 soldiers, who probably would have come from Rough Castle.

Images: Airborne Lens; Historic Environment Scotland