IT was an act of imperial aggression could have changed the history of Scotland, but has largely been forgotten to the mists of time.

Nowadays, it is popularly believed that the Romans had little to do with Caledonia, staying behind their defensive walls while getting on with colonising and civilising the rest of Britain.

But now a new book has shed light on the terrifying campaigns of Emperor Septimius Severus, whose ambition to conquer the ancient people north of Hadrian’s wall sparked genocide and almost extended the Empire to the foothills of the Highlands.

In ‘Septimius Severus in Scotland: the Northern Campaigns of the First Hammer of the Scots’, author Dr Simon Elliot has for the first time laid out the path taken by the legions as they put Scotland to the sword in the third century AD, and linked scientific data which shows the desolation they left behind.

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He believes that Severus set out to outdo his illustrious forbear, the Emperor Augustus, by extending Roman rule over both the ancient Persians and the Britons - and was only stopped by his own death in York before his plan could be completed.

Dr Elliott said: “Northern Britain and the lands that would become Scotland in the Roman period is the Wild West of the Empire - it’s one of the few remaining places the legions did not conquer.

“The poet Horace told Augustus that he would not become a God until he defeated both Parthia (Persia) and Britain, and when Severus he was finished with Parthia he turned his eyes north.”

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Trouble was brewing along Rome’s northern border in the year 207. Two tribal confederations - the Maeatae and Caledonians - had come together and were threatening to break through Rome’s defences.

Severus responded with an army of 50,000 legionaries, and a plan to crush the northern tribes and establish a Pax Romana once and for all.

Dr Elliott, a Trustee of the Council of British Archaeology, said: “It’s not clear if there really was a threat or if this was just the excuse to invade, but Severus made the most of the opportunity.

“These confederations had been bought off before and had become wealthy, and their elites and warriors had a taste for it and wanted more.

“There are also suggestions that there was a ‘harvest shock’ at the time, causing famine in the north and driving the tribes south.”

The Emperor Severus, along with his sons Caracalla and Geta, made their base at York and marched up the Roman road which ran to the Borders, “cauterizing all before it”.

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The route taken by Septimius' army. Reproduced from Dr Elliott's book

Each day a huge marching camp up to 70 hectares in size was built, making the Roman force untouchable.

After the Firth of Forth was reached, the Emperor crossed over the River Esk at Inveresk, reoccupying a fort at Cramond, near modern-day Edinburgh.

At some point, probably at South Queensferry, a bridge of 900 boats was built to allow the army to cross northwards, chasing the fleeing tribes who fought a guerilla campaign without resorting to a pitched battle they could not win.

But Dr Elliott says that Severus then divided his force into two, launching a blitzkrieg under Caracalla to seal off the Highlands, stopping at Bervie Water, 13km south west of Stonehaven.

The Emperor’s own force then made its move, heading north through Fife with camps at Auchtermuchty and Edenwood and a fort at Carpow on the River Tay, before he “slammed into the soft underbelly” of native resistance in the upper Midland Valley, brutalising the local population.

“This was Roman conquest as robbery with violence writ large,” Dr Elliot said.

Having secured peace - on Roman terms - Severus returned south only for the tribes to rise again the following year. This time, The Emperor stayed in York and gave command to Caracalla, ordering him to kill every man woman and child he encountered.

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Hadrian's Wall, as it appears today

Dr Elliott said: “We can imagine the scene when this astounding order was made - Severus seated at a podium in York quoting Agamemnon to his generals, telling them to ‘kill everyone, even the unborn in the womb’.

“This was genocide. Pollen records show returning woodland and there are signs of abandoned settlements. The people were gone.

“I think he was planning to absorb northern Britain, possibly right up to the Highland line, into the Roman empire. And if that had been a success we wouldn’t have the Scotland that we have today.”

But the writ of the Empire was not to last long. Severus died in York 211 and his sons immediately left for Rome to solidify their bids for the throne.

Scotland was pacified, but remained unconquered. And slowly the legions withdrew.

Dr Elliott said: “Whenever I’m giving talks, I always say that the Scots shouldn’t feel bad because they remain the one area of Britain which the Romans never conquered and occupied.

“Severus may have smashed his way through the country, but he didn’t make the natives bow down to Rome for very long.”

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Septimius Severus in Scotland: the Northern Campaigns of the First Hammer of the Scots, is published by Greenhill Books