The Antonine Conquest of Scotland
The nominated successor of Hadrian L. Aelius died in AD 138 and with Hadrian's death later that year Antoninus Pius became his successor. Immediatly it seems the Romans penetrated again into Scotland. The new governor Lollius Urbicus had to campaign in the Lowlands, the recently built frontier from Tyne to Solway was abanoned and a new barrier was to be installed along the Forth-Clyde isthmus. With the immediate abandonment of Hadrian's Wall by the emperor Antoninus Pius we gain the impression that Hadrian's frontier was a failure. But again there are several aspects leading to an advance in northern Britain. The building of a similar frontier clearly indicates that Antoninus Pius accepted Hadrian's frontier policy. So a suggestion is that Hadrian's Wall was a tactical success just built in the wrong place (Antonine Wall was about half the length of the southern barrier). There is also a convincing link to Claudius who started the conquest of Britannia. He needed a military success to settle himself to the imperial throne. The same seems appropriate for Antoninus Pius. He was not Hadrian's first choice and he had no military experience: so a successful campaign in Britain would give him the needed military prestige to secure his position (the army played always an important part concerning the maintenance of the emperor). Antoninus Pius only got two imperial acclamations for victories in Britain and Germany at the beginning of his reign. This fact indicates that he had to gain victories for his prestige and to settle himself in his position. On the other hand a campaign in Britain without any other reasons seems unlikely. The strategical advantage of Antonine Wall (only 40.5 Roman miles from ocean to ocean) was mentioned above. Even economic reasons could have influenced the decision to advance further north, since the most fertile land in northern Britain are the Lowlands of Scotland (especially the territory of the philo-Roman Votadini). Maybe a minor unrest in Britain focused the emperors interest on this province and together with the strategical and economic advantages he decided to gain his victory in Scotland.
The Emperor Antoninus Pius	Antonine Wall from the Air	Antonine Wall west of Rough Castle
So probably still in AD 138 the advance north was planned and the governor Lollius Urbicus seemed to act very fast. In the Lowlands the fort distribution is basicly next to Agricolan sites with a focus on the two main roads leading north (Dere Street in the east and the western road Annandale-Clydesdale). The forts in the Lowlands were to control the native population, especially the Dumnonii and the Selgovae needed close supervision. The conquest of Lowland Scotland must have taken place between AD 139 and 142 since Antoninus Pius was claimed imperator for his victory in AD 142. Possibly the construction of the Antonine Wall started under Lollius Urbicus but it was definitely finished by his predecessor. After the new northern frontier was installed Hadrian's Wall was abandoned and opened to public traffic. Some wall forts remained obviously occupied because of military reasons (maybe they were occupied by legionaries). Now again the Stanegate became more important for the east-west communication.
Construction and Modifications Occupation and Retreat Function of the Frontier