Roman fort in Pembrokeshire may back a medieval legend

A newly discovered Roman fort in the Preseli Hills of Pembrokeshire could show that a medieval Welsh legend about a Roman emperor was based on real events, archaeologists say.

Magnus Maximus ruled Britain in the late fourth century and led his troops against the Picts and Scots. The Mabinogion, a collection of medieval Welsh tales, describes how, as Macsen Wledig, he pitched his camp at Frenni Fawr, the 395-metre easternmost peak of the Preseli Hills. Until now there was no archaeological evidence for a Roman camp or fort there.

The discovery

Dr Mark Merrony, a Roman specialist at the University of Oxford, spotted the outline of the fort on satellite images of an overgrown field about two miles south-west of the summit in 2024. Shortly after visiting, he found a Roman tile, the first of many.

An excavation funded by Oxford University and crowdfunding has just finished, and among its finds were two coins from the late fourth century, the period of Magnus Maximus. Dr Merrony said his brother, Nick, had jokingly asked him to find a couple of coins to prove the theory, and then turned them up himself.

"If Magnus Maximus was there, there must have been an army there," Dr Merrony said. "The presence of a heavily fortified Roman auxiliary fort may help unlock the mystery of a Mabinogion legend that has endured for nearly 1,700 years."

What has been found

The fort measures 180 by 150 metres and sits on a slope with a commanding view. It probably held about 500 troops. It has the classic Roman "playing-card" shape with rounded corners, and a road running at right angles to it.

Finds so far include an unusual iron writing stylus, pottery fragments, large quantities of Roman tiles and compacted clay floors, a common feature of military sites. Even the ruts left by wagons have survived. A geophysical survey revealed a building in the centre, consistent with a headquarters facing east "towards the enemy", and a larger building to the south, probably the commander's house.

Rethinking Roman Wales

The fort challenges the idea that the local Celtic tribe lived peacefully alongside the Romans. Dr Merrony identified a Roman road along the southern shoulder of the Preselis in 2022, which also challenged assumptions that the Romans did not venture far into west Wales. His previous discoveries include two Roman villas.

How archaeologists date sites

Coins are among the most useful finds for dating a site, because Roman coins carry the image and name of the emperor who issued them, and their production dates are well known. A coin shows that a layer cannot be older than the date it was minted, although coins could stay in circulation for many years.

Satellite imagery, aerial photography and geophysical surveys, which detect buried walls and ditches without digging, have transformed the search for Roman sites in recent decades, revealing forts, camps and roads that had left no trace above ground.

Further excavations are planned, and the research will appear in the archaeology magazine Antiqvvs. The Preseli Hills are already famous as the source of the bluestones at Stonehenge, carried about 150 miles to Salisbury Plain some 5,000 years ago.