By the year 50AD most of southern England had fallen to the soldiers of Rome. In the wild areas of the west, however, the legions had made little progress and the Welsh tribes, the Silures and the Ordovices in the south, the Demaete in the north, kept up an almost constant guerilla campaign against the invaders.
The date is not exactly clear but in around 57AD the Roman general Suetonius Paulinus decided that enough was enough. He led his legions out from the fortress town of Chester, heading for a final reckoning on the island of Anglesey, or Mona as it was then known.
The island was doubly significant for the defending tribesmen. To begin with Anglesey was the sacred home of the druids, the spiritual leaders of the native people. Many, if not most, of the druids actually lived there and were certainly on the island when Suetonius attacked.
Secondly, the island was a very handy bolt hole where tribesmen fleeing from the Roman rule - or persecution, as they saw it - could find a home and shelter. The place was, the Romans felt, therefore a potential source of unrest.
In addition, the Romans – always a superstitious people – believed that on Anglesey the druids practiced all sorts of weird and evil rituals. Magic and soothsaying, even human sacrifice, they told themselves, were carried out on this distant island. The Romans were hardly paragons of virtue but such beliefs were commonly held amongst the troops at this time.
And so Suetonius Paulinus set off. What happened next was described in some detail by the Roman historian Tacitus.
Tacitus was probably not present at the battle, but he was a scrupulously accurate researcher and historian, and would have used first hand accounts from men who were there, at both the campaign and the eventual battle, to lend credibility to his account.
The Romans headed steadily westwards and the tribesmen of the area, realising they could not stand against such a mass of highly trained and well-equipped soldiers, simply slipped away into the hills. They might have made the occasional foray against isolated units of the advancing army but, other than that, there was little opposition.
Eventually Suetonius Paulinus and his legions reached the shores of the Menai Straits. Knowing that the time had come to make a final stand, the tribesmen and their priests gathered on the opposite shore of the island.
Tacitus gave the following description: "On the shore stood the forces of the enemy, a dense array of arms and men, with women dashing through the ranks like the furies --- The druids pouring forth dire imprecations with their hands uplifted towards the heavens, struck terror into the soldiers."
The druids, the supposedly human-sacrificing enemy priests, struck a chill in everyone's hearts, but it was the appearance of the women, wild haired and all bearing torches, that most frightened the legionaries. They were not used to facing such an enemy.
Such fear did not last long. Urged on by their officers, the Roman cavalrymen swam their horses across the Straits while the infantry made the crossing in small, flat-bottomed boats. And when they reached the Anglesey side, their blood-lust knew no bounds.
Tacitus simply said: "they bore down upon them, smote all who opposed them to the earth and wrapped them in the flames they had themselves kindled."
What happened was a massacre. Men, women and children - armed and unarmed, young and old - fell under the swords of the Romans. The bodies of the dead and dying were unceremoniously hurled onto makeshift funeral pyres.
Suetonius and his soldiers then roamed across the island, destroying the druids sacred oak groves, smashing their altars and temples and killing anyone they could find.
The Roman general next proceeded to establish a garrison on Anglesey, a military fortress that kept the native tribes in total subjugation. Rebellion in other parts of Britain soon took Suetonius away from the western lands and it was another 20 years before Wales was totally conquered.
Yet by his actions on Anglesey, Suetonius Paulinus smashed the heart out of Welsh resistance and with the demise of the druids the people of Britain had lost their spiritual driving force.
The story of the massacre of the druids and their defending tribesmen is one of barbarity and outright cruelty. It was undoubtedly fostered by superstition and ignorance on the part of the invaders – but then, so many crimes against humanity usually are.