Calgacus (also sometimes called Calgacos or Galgacus) lived from - very roughly - AD50 to AD100, if he lived at all. He was the leader of the Caledonians who fought against the Romans at the Battle of Mons Graupius in AD84. The wider picture in Scotland at the time is set out in our Historical Timeline.
Calgacus appears as an important character in the biography of the Roman Governor of Britain, Julius Agricola, De vita et moribus Iulii Agricolae, written by his son-in-law, Tacitus, in AD98. Nothing else is known about him from any other source, and there has to be some question about whether he actually existed at all. But if he didn't then someone like him probably did. His name means "the swordsman".
Julius Agricola began his campaign to conquer the land we now call Scotland in AD80. By the beginning of AD84, they controlled everything up to Tayside, and in that year pressed still further into northern Scotland, trying to draw the main forces of the Caledonian leader Calgacus into open battle. The Caledonians, however, were intent on maintaining their hit-and-run tactics. But when Agricola's troops captured many of the storehouses holding the Caledonians' recently gathered harvest, Calgacus had to choose between fighting, or letting his people starve in the forthcoming winter. The final showdown occurred at the Battle of Mons Graupius, apparently in Autumn AD84.
The location of the battle is the subject of wide debate today, with candidates including Bennachie in Aberdeenshire and the Gask Ridge west of Perth; though locations as far afield as Moray, Fife and Sutherland have also been suggested. While Tacitus was a little vague about geography, he is more definite about the conduct of the battle itself. According to him the Caledonians mustered some 30,000 men to face the 20,000 Roman legionnaires and auxiliaries under Agricola.
The battle started with an exchange of missiles before the 8,000 Romans auxiliaries in the Roman front line attacked uphill, closing with the Caledonians to neutralise the latter's longer swords. The 3,000 Roman cavalry then outflanked the Caledonians, causing them to break and flee. The main body of the Roman army at Mons Graupius, the 9,000 men of the legions, were held in reserve and took no active part in the battle. By Tacitus's account, the battle cost the lives of 10,000 Caledonians and just 360 Romans. The remaining 20,000 Caledonians simply melted away into the hills. No mention is made of the death or capture of Calgacus, so it seems that he was among those who survived, and whose lurking presence in the mountains helped ensure the Romans never did conquer Scotland.
To modern eyes, one aspect of Tacitus's coverage of the Battle of Mons Graupius stands out as especially odd. According to Tacitus, Calgacus gave a speech to his army before the battle. In it he said:
"Whenever I consider the origin of this war and the necessities of our position, I have a sure confidence that this day, and this union of yours, will be the beginning of freedom to the whole of Britain. To all of us slavery is a thing unknown; there are no lands beyond us, and even the sea is not safe, menaced as we are by a Roman fleet. And thus in war and battle, in which the brave find glory, even the coward will find safety. Former contests, in which, with varying fortune, the Romans were resisted, still left in us a last hope of succour, inasmuch as being the most renowned nation of Britain, dwelling in the very heart of the country, and out of sight of the shores of the conquered, we could keep even our eyes unpolluted by the contagion of slavery. To us who dwell on the uttermost confines of the earth and of freedom, this remote sanctuary of Britain's glory has up to this time been a defence. Now, however, the furthest limits of Britain are thrown open, and the unknown always passes for the marvellous. But there are no tribes beyond us, nothing indeed but waves and rocks, and the yet more terrible Romans, from whose oppression escape is vainly sought by obedience and submission. Robbers of the world, having by their universal plunder exhausted the land, they rifle the deep. If the enemy be rich, they are rapacious; if he be poor, they lust for dominion; neither the east nor the west has been able to satisfy them. Alone among men they covet with equal eagerness poverty and riches. To robbery, slaughter, plunder, they give the lying name of empire; they make a solitude and call it peace."
Setting aside the likelihood of the Roman Governor's son-in-law being allowed within earshot of Calgacus's pre-match pep talk, these are very odd sentiments to appear in Tacitus's biography of Agricola. Setting even that aside, the reported speech seems to owe much more to heroic fiction than to accurate reportage. Indeed, some of this begins to sound remarkably like the pre-battle speech put into the mouth of the character of William Wallace by the scriptwriter for the film Braveheart. But history is what people agree to believe, so perhaps we should just be grateful that Scotland has had two such remarkable orators at different points in its history...