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A Roman fort discovered in Gwynedd is changing what we know about the history of Wales.

The fort was discovered on the Llyn Peninsula this summer, in an area previously thought to have been free from direct Roman occupation, with no previous evidence of military structures on the peninsula at all.

The discovery was made by senior aerial investigator at the Royal Commision for the Ancient and Historical Monuments of Wales, Dr Toby Driver, who was flying over the peninsula during the recent heat wave.

During periods of prolonged dry weather the remains of buildings below ground can become visible as the vegetation above dies off leaving outlines in the scorched earth.

(Image: RCAHMW)

Dozens of discoveries were made this summer but few could prove to be as historically significant as this one.

“The Royal Commission flight on July 10 was lucky enough to discover what looks like a Roman fort near the coast in western Llyn,” said Dr Driver.

“This is a landscape which has been intensively flown for cropmarks (buried archaeological sites) for 40 years and we know where most of the sites are.

“It was a real surprise to come up with a previously undiscovered site.

"It immediately looked Roman, and so is 20 miles at least from the nearest known Roman forts which occupy the western fringes of Snowdonia, between Trawsfynydd and Caernarfon.

“If confirmed as Roman, it will be the first Roman military installation on the Llyn Peninsula.”

How do they know it was a Roman from the air?

(Image: Crown Copyright RCAHMW)

Despite having an empire that stretched from Egypt to Scotland the Romans built their forts from a manual.

This means that soldiers in Syria would be able to find their way round a camp in Anglesey.

It is this uniformity that helps identify the site.

“I really couldn’t believe that I was seeing a possible Roman watchtower,” he said.

“The plan revealed in the parched grass – a playing card shaped double-ditched square enclosure encircled by a wider outer ditch – very similar to a site surveyed by the Gwynedd Archaeological Trust on the north of Anglesey.

“It looks like these were 1st century AD Roman military installations on the coast of north-west Wales designed to overlook good beaches and natural harbours, allowing Roman soldiers and officials to oversee coastal trade and communications.”

How much do we know about the Roman occupation of Wales?

(Image: RCAHMW)

“The Iron Age people of Wales left no written documents, but descriptions of their history are preserved thanks to a particular Roman historian who sought to document the conquest of Britannia,” said Dr Driver.

“Through the writings of Senator Tacitus (56-117 AD), we have a few tangible glimpses of the running battles, family histories and changing political strategies which marked the long years of the conquest of Britain, including the western lands which would later become Wales.

“These military actions began with the invasion at Richborough in Kent by Emperor Claudius in 43 AD, but were not concluded until nearly thirty years later with the decisive campaigns of Governor Sextus Julius Frontinus between 74 and 77 AD, which brought Wales under control.

“Frontinus was succeeded in 77 AD by the skilled tactician Agricola, the father-in-law of Tacitus and Governor of Britannia, who swiftly defeated the Ordovices in mid and north Wales, conquered Anglesey and went on to oversee the construction of a network of Roman forts in Wales and beyond.

“The Cardigan Bay region and north-west Wales effectively enjoyed a twenty-year respite from the Roman military penetration seen in other parts of Wales to the east and south, and was finally brought under control in the late AD 70s.

“The Romans were skilled mariners and charted the coastline of Britain early after the conquest.

"They understood that north-west Wales has rich resources including copper and gold.”

What is going to happen with the site now?

(Image: RCAHMW)

The risk with sites like this is that they could be disturbed before they can be properly excavate it.

For that reason the RCAHMW are deliberately vague about the exact locations of sites.

“The site lies on private land,” said Dr Driver. “We hope to work with the landowner to undertake a geophysical survey, to ‘see through the soil’ and discover a better plan of the site.

“At that stage we will be able to be more sure if the site is a Roman military installation, or something else.”

This map shows the location of the crop marks found in Wales