How did Septimius Severus campaign in Caledonia?

In 208 CE, the emperor Septimius Severus arrived in Britain accompanied by his sons, Caracalla and Geta, to subdue regions of the island that remained outside of Roman control. His military campaign in Caledonia lasted from 208 to 211 CE.123

During this period, the Roman military engaged in active campaigning that involved the construction of permanent bases along the east coast of Scotland. These efforts were focused on the area beyond Hadrian’s Wall, which had previously served as the fixed frontier.34

Following the death of Septimius Severus at Eboracum (modern-day York) in 211 CE, his successor, the emperor Caracalla, shifted the Roman strategy from direct military occupation to the regulation of relationships through treaties. These agreements were potentially supported by subsidies and enforced by supervising the Lowlands using patrols based in forts located beyond the wall.31