The Roman invasion of Caledonia was launched in 208 by the Roman emperor Septimius Severus.

Preparation

The cause of Severus’ invasion of Caledonia (modern day Scotland) was a massive increase in raids and attacks on Roman Britain.
In 208, Severus arrived in Britain with around 40,000 men and marched north to Hadrian’s Wall.
Severus marched north and occupied all the land between Hadrian’s Wall and the Antonine Wall.
After completing the occupation Severus began another reconstruction project but this time on the Antonine Wall.
Severus built a 165-acre (67 ha) camp south of the Antonine Wall at Trimontium, probably assembling his forces there.
Supported and supplied by a strong naval force, Severus then thrust north with his army across the wall into Caledonian territory.

Invasion of Caledonia

In 209, Severus led his army north into the highlands and roughly marched the same way Agricola had invaded over 100 years before.
Severus suffered heavy casualties due to the guerrilla tactics used by the Caledonians.
To counter this, Severus began a plan of holding down all the territory he could by the reoccupation of many of Agricola’s old forts and devastating all the territory he couldn’t.
This led to many of the tribes attempting to reach a peace agreement with Severus because of fear of extinction through Roman genocide.
Peace talks failed and it looked as if the war would continue until all the tribes had submitted to Rome or been exterminated.
He was now intent on exterminating the Caledonians, telling his soldiers: “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 early 210 Severus’ son Caracalla led a punitive expedition north of the Antonine wall with the intention of killing everyone he came across and looting and burning everything of value.

Retreat & Aftermath

The plan was for Severus to follow his son’s army and permanently occupy all of Caledonia.
In 210, Severus became ill and went to York to rest and recover. He kept getting worse until 4 February 211 when he died.
Caracalla then called off the war against the Caledonians and headed back to Rome to consolidate his power.
The Romans never campaigned deep into Caledonia again because they lacked spare forces to continue dealing with attacks as most manpower was redirected to secure other occupied lands.
They soon withdrew south permanently to Hadrian’s Wall.
Although Caracalla withdrew from all the territory taken during the war, the latter did have some practical benefits for the Romans.
Which includes rebuilding of Hadrian’s Wall which once again became the border of Roman Britain.
The war also led to the reinforcing of the British frontier, which had been in dire need of reinforcements, and to the weakening of the various Caledonian tribes.
It would take many years for them to recover their strength and begin raiding in strength.