23. Was Hadrian’s Wall always the most northerly frontier of Roman Britain?

No. Soon after Hadrian died in AD 138 and he was succeeded by his adoptive son, Antoninus Pius, work began on a new mural barrier across the Forth–Clyde isthmus. This time, like the Turf Wall, it was an earthen rampart on a stone base, but it was also much shorter, with fewer and smaller forts, and would have required fewer men to garrison it. However, it was abandoned within 25 years of its construction and Hadrian’s Wall was recommissioned as the most northerly frontier in the Roman Empire.

Further reading: Breeze and Dobson 2000