The Romans invaded Scotland/Caledonia three times, and though they were successful, and established a system of roads and camps/forts as far up the east coast as what would one day be Inverness, they didn’t remain, primarily because they were not able to live off the land. The supply and logistics train was so long that even the legions were challenged to supply the outposts that they established.
Because they didn’t move fast – the Romans engineered their way through campaigns, the first Northern Campaign under Governor Agricola, lasted five years (80 AD – 84 AD) and finally brought the Picts to battle in the Battle of Mons Grauplus.
Ensuing raids and counter raids seemed endless to the legions in Northern Britiania and resulted in Emperor Hadrian’s order to construct a (big beautiful) wall across the island, from what is Carlisle to Newcastle today.
These are artists renditions of what Roman fortifications might have looked like during construction and upon completion. Note the Mile Forts (1000 paces apart).
The expense of maintaining Antonine’s Wall (a turf wall, not a stone wall) were too great and the Roman Army withdrew further south, shortening their lines of supply and communications to Hadrian’s Wall.
Due to near constant raiding across the wall from Scotland, Septimius Severus ordered an invasion of Scotland in 208 AD.
During this campaign, the Roman Army used infrastructure that had been laid down literally centuries before, and improved it. However well they campaigned, there was simply not enough of a local economy to support the legions in the field. The population density of Scotland was too small, and the crops they produced were insufficient to be worth the cost of importing supplies (primarily supplied by sea).
Cassius Dio wrote of Serverus’ campaign in Scotland:
Serverus, accordingly, desiring to subjugate the whole of the land, invaded Caledonia. As he advanced through the countryside, he experienced countless hardships while cutting down the forests, leveling the heights, draining the swamps and bridging rivers. In the process, he fought no battle and beheld no enemy in battle array. The enemy purposely put sheep and cattle in front of the soldiers for them to seize in order that they might be lured on further until they were worn out. For the water caused great suffering to the army, and when they became scattered, they would be attacked.
Winter rain (almost constant) wore the army down and in order to defend the wider area, Serverus disbursed the army to allow it to forage. They lost fifty-thousand soldiers during the campaign to disease, and the pressure of raids on the outposts that had been established without once bringing the enemy to battle. Cassius Dio continues:
But Severus did not desist until he approached the extremity of the island. There he observed most accurately the variation of the Sun’s motion and the length of the days and the nights in summer and winter respectively. Having traveled on a covered liter most of the way due to his infirmity), he returned to the friendly portion after he forced the Britons to come to terms, on the condition that they abandon a large part of their territory.
Severus did what many generals and leaders have done since his time. Having lost 50,000 men and untold equipment over the campaign, he declared victory and abandoned the land that he conquered.
Cassius Dio describes Scotland and the Britons:
They inhabit wild and waterless mountains and desolate, swampy plains. They possess neither walls, cities nor tilled fields, but live on their flocks, wild game and certain fruits. 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 their 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 short spear, with a bronze apple attached to the end of the spear shaft, so when shaken, it may clash and terrify their enemy. They also have daggers. They can endure hunger, cold, and any kind of hardship, for they plunge into swamps and exist there for many days with only their heads above water. In the forests, they support themselves upon bark and roots. For all emergencies they prepare small portions of beans which prevent them from feeling hunger or thirst.
The Romans didn’t find much worth conquering in Caledonia (Scotland).