No sooner had Hadrian's Wall been completed than his successor, Antoninus Pius decided to go on the offensive in Britain. It's easy to guess the feelings of the people who had built the Wall to this news. This was an especially surprising decision, as generally Antonnius Pius followed Hadrian's policies. In fact it was also the one notable example in his reign of a deliberate offensive to gain territory.
The strategy may have been a response to raids by the Britons. However another possibility is that Pius may not have felt secure in his succession to Hadrian, especially as he lacked military experience. A campaign in Briton could bring him prestige with the military, it also had the advantage that if things went wrong it was a long way from Rome. The importance that Pius attached to the campaign is shown by this being the only time he took the title imperator (victorious general) as emperor.
Whatever the reason one of the emperors first acts was to appoint Q.Lollius Urbanicus as governor of Britain. He immediately went to work rebuilding the base at Corbridge. This was an idea jumping off point for an invasion of Scotland. By 143 the Romans were celebrating a victory, and a new Wall was under construction 100 miles North of Hadrian's Wall between the Firth of Clyde and the Firth of Forth.
The Antonine Wall.
The Antonine wall was constructed from earth rather than stone. It used the lessons learnt from Hadrian's Wall in that the forts were built into the wall. There were also outlying forts to the north of the Antonine Wall. One major advantage it had over Hadrian's Wall was that it was about half the length, despite this it had roughly the same size garrison as Hadrian's Wall and so was held in about double the strength per mile.
The reoccupation of southern Scotland was supposed to be permanent, on Hadrian's wall sections of the vallum were dug through and the gates taken off the milecastles so as to restore free passage across the wall. However if the Romans thought that this victory would bring peace to Britain they were to be sorely disappointed; instead it was to usher in a period of nearly sixty years of warfare in the north of Britain.
Trouble again broke out in the 150s, the exact nature of this is unclear but an inscription in Newcastle records the arrival of reinforcements for all three legions in Britain. The situation must have been serious because the Antonine Wall was abandoned and Hadrian's Wall was refurbished.
At some point the Antonine Wall was reoccupied. The exact date for this is uncertain although it was probably within a few years of it being abandoned. Pius would not have been happy to see his major achievement lost, and so it may have been before his death in 161 that the Antonine Wall was reoccupied.
Antoninius Pius was succeeded as emperor by Marcus Aurelius who is remembered as the philosopher emperor. At the onset of his reign many disasters struck the empire, with attacks in the East, the Rhine and most seriously the Danube. In 166 a barbarian attack was to actually penetrate northern Italy. These attacks were the forebears of the attacks that would continue to convulse Rome's frontiers for the next century. These attacks elsewhere in the empire must have taken all the effort of the Emperor and reduced the likelihood of major campaigns in Britain.
Although it is difficult to know the exact timing of events, its likely that the Antonine Wall was abandoned early in Marcus Aurelius reign, and that the frontier was again back at Hadrian's Wall. The new governor Calpurnius Agricola is likely to have been sent out to implement these changes, his name has been found on a large number of inscriptions along the Wall. However one major change to previous withdrawals was that significant forces were retained in the south of Scotland.
One notable event that happened in Marcus Aurelius reign came from his campaign on the Danube against the Sarmatians. On concluding a peace treaty, the Sarmatians agreed to supply 8,000 cavalry men to the Roman. Of these 5,500 were sent to Britain. The Sarmatians were famous for their heavy armored cavalry, and their presence would have been a substantial boost to the army in Britain (as well as keeping the Sarmatians well out of the way!).