In AD 79 Agricola, the Roman governor of Britannia, sent a fleet to survey Scotland's coast. As Agricola advanced, conquering southern Scotland by AD 83, the Caledonian tribes faced imminent invasion.
According to the Roman historian Tacitus, the Caledonians then "turned to armed resistance on a large scale", attacking Roman forts and skirmishing with their legions. In a surprise night-attack, the Caledonians very nearly wiped out the whole 9th legion until it was saved by Agricola's cavalry.
In the summer of AD 84 Agricola advanced into the Caledonians' stronghold in the north-east, hoping to force battle. Somewhere on this march, at a place called Mons Graupius (the Grampian mountains), the Caledonians confronted them.
Everything depended on this encounter. 30,000 Caledonians faced a Roman army about half that size, they also held the higher ground, but they lacked the organisation and military tactics of a Roman legion.
The Romans were tightly disciplined and relied on a short stabbing sword in combat. Their front line was made up of Germanic auxiliary troops from Holland and Belgium, with the Roman legionaries in the rear. Brutal hand to hand fighting must have followed. At one point the Caledonians, using their greater numbers, outflanked the Romans only to meet hidden Roman cavalry suddenly closing on them.
Any hopes of a Caledonian victory vanished. Tacitus claims that 10,000 Caledonians were slaughtered in the battle. Many fought valiantly to the end, more fled into the surrounding woods and hills, burning their houses, or, in fear of Roman reprisals, even killing their own wives and children.
The following day Tacitus tells us, "...an awful silence reigned on every hand; the hills were deserted, houses smoking in the distance, and our scouts did not meet a soul."
In the wake of defeat at the Battle of Mons Graupius, as winter drew in, the Caledonians must have considered themselves doomed, but then Roman politics intervened. The Emperor Domition ordered Agricola back to Rome. For Tacitus, Agricola's son-in-law, Scotland had been "let go", however Rome was facing a more pressing military crisis on the Rhine and Danube frontiers.
In 122 AD Hadrian's Wall was built between the Solway and the Tyne, establishing a frontier for the Empire. Hadrian's successor as emperor, Antoninus Pius, pushed the frontier further north to the Forth/ Clyde isthmus and built his own wall, the Antonine Wall. This was built mainly for the prestige of expanding the Empire, but on his death it was abandoned in favour of Hadrian's Wall.
Faced with so formidable an opponent, the northern tribes united into the Pictish nation. The Picts' name first appears in 297 AD and comes from the Latin Picti, literally "painted people". By 306 AD the Emperor Constantius Chlorus was forced to subdue his northern frontier in the face of Pictish attacks on Hadrian's Wall. However, the tide was slowly turning against the Roman Empire.
As Rome weakened the Picts became bolder. In 360 AD they allied with the Gaels from Ireland and launched a concerted invasion across Hadrian's Wall. Julian, the last pagan Emperor of Rome, sent legions to deal with them but to little effect. Within four years they were raiding deep inside Britannia until they were finally repelled by Theodosius the Elder, father of the emperor of the same name who made Christianity the only official religion in the Empire in 367.
The Roman system of controlling of the tribes north of Hadrian's Wall broke down. Scouting was abandoned and forts like Newstead north of Hadrian's Wall were left deserted. Hadrian's Wall itself was eventually abandoned and in 411 AD the legions departed to deal with the barbarian crisis at the heart of the empire.
The Romano-Britons continued to appeal to Rome for help. Eventually they hired other barbarians, the Angles and Saxons, to assist in their defence against the Picts and other raiders. In one of the great ironies of history the Scottish tribal raids on the Romano-Britons helped to bring the peoples who created England to this island.