In 208, Septimius Severus launched a large military campaign against the Caledonians in Britannia. Cassius Dio writes that the reason for the invasion was that “his sons were changing their mode of life and that the legions were becoming enervated by idleness”. Herodianus’ explanation is a bit more convincing: the Roman governor Lucius Alfenus Senecio had reported “that the barbarians there were in revolt and overrunning the country, looting and destroying virtually everything on the island”. Now that may have been somewhat of an exaggeration, but it is quite likely that when Clodius Albinus crossed over to Gaul in 195, he took with him most of the legions and auxiliaries on the island. This would have left especially the northern part of Roman Britain vulnerable to Caledonian raids. We should also remember that there had been Caledonian raids into Roman Britain under Commodus.
It is unlikely that the Romans had to deal with a full-scale Caledonian invasion, but raids across the border and perhaps the temporary loss of control of Hadrian’s Wall, like in 184, would have been a sufficient casus belli for the now aging emperor. Despite suffering badly from gout since his Parthian campaign, Severus chose to go to Britannia himself. Caracalla and Geta, his two sons who were already frequently at each other’s throats, went with him. Severus thought it would be good for them to be away from Rome for a while and lead the simple life of a soldier on the march. He was wrong.
Both Herodianus and Casius Dio have left us colourful descriptions of the people whom the Romans were about to fight.
“Strangers to clothing, the Britons wear ornaments of iron at their waists and throats; considering iron a symbol of wealth, they value this metal as other barbarians value gold. They tattoo their bodies with coloured designs and drawings of all kinds of animals; for this reason they do not wear clothes, which would conceal the decorations on their bodies. Extremely savage and warlike, they are armed only with a spear and a narrow shield, plus a sword that hangs suspended by a belt from their otherwise naked bodies. They do not use breastplates or helmets, considering them encumbrances in crossing the marshes.”
“There are two principal races of the Britons, the Caledonians and the Maeatae, and the names of the others have been merged in these two. The Maeatae live next to the cross-wall which cuts the island in half, and the Caledonians are beyond them. Both tribes inhabit wild and waterless mountains and desolate and swampy plains, and possess neither walls, cities, nor tilled fields, but live on their flocks, wild game, and certain fruits; for they do not touch the fish which are there found in immense and inexhaustible quantities. They dwell in tents, naked and unshod, possess their women in common, and in common rear all the offspring. Their form of rule is democratic for the most part, and they are very fond of plundering; consequently they choose their boldest men as rulers. They go into battle in chariots, and have small, swift horses; there are also foot-soldiers, very swift in running and very firm in standing their ground. For arms they have a shield and a short spear, with a bronze apple attached to the end of the spear-shaft, so that when it is shaken it may clash and terrify the enemy; and they also have daggers. They can endure hunger and cold and any kind of hardship; for they plunge into the swamps and exist there for many days with only their heads above water, and in the forests they support themselves upon bark and roots, and for all emergencies they prepare a certain kind of food, the eating of a small portion of which, the size of a bean, prevents them from feeling either hunger or thirst.”
The Caledonians may have sent a delegation to offer peace, but Severus flatly refused to negotiate with them, as he planned to subjugate the whole island. The emperor left Geta behind in the south and then marched north with Caracalla and his invasion force, adding elements of Roman forces already on the island to his own army. We unfortunately have limited details about Severus’ campaign. If control of Hadrian’s Wall had indeed been lost, it is likely Severus re-won control of it and then crossed it into Caledonian territory. We know that he strengthened Hadrian’s Wall, turning it into a more formidable barrier completely made of stone.
North of the wall, the marshy terrain would have been the Romans’ greatest enemy. Herodianus writes that Severus “saw to it that dikes were provided in the marshy regions so that the soldiers might advance safely by running on these earth causeways and fight on a firm, solid footing”. It has been possible to reconstruct the route the Roman invasion force took. The Romans penetrated deep into Caledonian territory. Nevertheless, there would be no great and decisive battles, only skirmishes and confrontations between Caledonian raiding parties and Roman patrols. This was a guerrilla war. The Romans made gains and marched further north than ever before, but they could never firmly control all the territory they took.
The war must have taken a terrible toll on the Caledonians, many of whom were massacred. The Romans suffered heavily as well, with Cassius Dio mentioning the slightly incredible number of 50.000 Roman casualties (which is probably larger than the entire invasion force!). The emperor was suffering badly from his gout and had to be carried in a chair. To make things worse, there was at least one – alleged – attempt by Caracalla to murder his father.
In any case, both warring sides probably agreed to peace somewhere in 209, only to begin hostilities again the next year. Severus was now so ill that he sent Caracalla north with the army with orders to kill anyone that they might encounter. The emperor added a verse from Homer’s Iliad, which he slightly amended:
“Let no one escape sheer destruction,
No one our hands, not even the babe in the womb of the mother,
If it be male; let it nevertheless not escape sheer destruction.”
(in the original version, the line reads: “Let none escape death at our hands, not even the child in the womb; let not a one survive, let all Ilium die: leave none behind as witnesses to mourn.”- these are words spoken by Agamemnon to his brother Menelaus, who is about to spare an enemy’s life)
Caracalla’s campaign took place in early 210, possibly north of the Antonine Wall. It was the emperor’s intention to follow his son north once he got better again. But Severus never recovered and he died at Eburacum (present-day York, way south of Hadrian’s wall) on 4 February 211. That was the end of the war, as his sons had no intention of continuing it. They made peace with their adversaries, abandoned all territorial gains between the Antonine Wall and Hadrian’s Wall, and withdrew behind the later. It may be around this time this the division of Britannia into two separate provinces was formalised. These provinces would remain largely peaceful for the remainder of the third century.
– Adrian Goldsworthy, The Fall of the West, p. 67-69.