Archaeologists have identified a fourth-century Roman fort in Pembrokeshire, Wales, that may provide physical evidence supporting medieval Welsh legends about the Roman emperor Magnus Maximus. The discovery, led by Dr. Mark Merrony of the University of Oxford, sheds new light on longstanding folklore surrounding the emperor’s activities in the region.

Magnus Maximus, who ruled Britain during the late Roman period, is known from historical accounts to have campaigned against northern tribes such as the Picts and Scots. Medieval Welsh literature, particularly the Mabinogion—a collection of mythic and epic tales—depicts Maximus, referred to as Macsen Wledig in Welsh, establishing a military camp near Frenni Fawr, a 395-metre peak at the eastern end of the Preseli Hills. Until now, no archaeological site had been definitively linked to these stories.

The fort was uncovered in 2024 approximately two miles southwest of Frenni Fawr’s summit after Merrony identified a distinctive outline on satellite imagery of an overgrown field. Initial findings, including Roman tiles and a rare iron stylus, prompted further excavation work, supported by Oxford University and public crowdfunding. Among the artifacts recovered were two late fourth-century Roman coins discovered by Merrony’s brother, which appear to correspond chronologically with Maximus’s rule.

Measuring about 180 by 150 metres, the site is believed to have housed around 500 soldiers, based on its size and defensive features. The fort’s layout, described as having rounded corners resembling a playing card, includes a perpendicular road within its enclosure. Geophysical surveys revealed a rectangular structure in the centre of the fort and a larger building to the south. Merrony suggests these correspond to a headquarters building, oriented eastward to face potential attackers, and a commander’s residence.

Previous assumptions have held that the Indigenous Celtic tribes inhabiting the area near the Preseli Hills may have maintained relatively peaceful relations with Roman forces. However, the presence of a substantial auxiliary fort suggests a more militarised Roman presence in this remote part of Wales than previously believed. Merrony’s earlier work includes identifying a Roman road along the southern slopes of the Preselis, challenging views that Roman influence did not extend deeply into the Welsh interior.

While the archaeological finds do not conclusively prove every detail of the Mabinogion’s narrative, the discovery offers tangible support to the idea that historical events inspired the medieval legends of Magnus Maximus in Wales. Merrony plans to publish full details of the excavation in the journal Antiquvs and will include the findings in his forthcoming book, Lives of the Roman Emperors: From Augustus to Romulus Augustulus. The site contributes to a growing understanding of Roman military strategy and presence in Britain’s far west during the late Empire.