The Antonine Wall was the most northern frontier of Roman Britain, stretching from the Firth of Forth to the Firth of Clyde in Scotland. It was 39 miles long, half the length of Hadrian's Wall. Although the Roman army fought in Scotland from as early as the 1st century AD, the frontier was not built until the reign of the Emperor Antoninus Pius (AD 142-55). The Antonine Wall was abandoned after twenty years, when the Roman army withdrew from Scotland in AD 164, pulling the northern frontier back down to Hadrian's Wall. After invasions from the north in AD 197, the emperor Septimius Severus arrived in AD 208 to restore order along the Scottish borders, briefly reoccupying and repairing portions of the Antonine Wall.