It runs for 120 kilometres from the River Tyne to the shore of the Solway Firth, some miles south of the border between modern England and Scotland, nearest at the western end. For much of its length, the wall can be followed on foot.
It was built by the soldiers of the Roman legions stationed in Britain starting in AD 122 after a visit by Roman emperor Hadrian. It was the northern border of the Roman Empire on that island for most of the Roman Empire's rule. It replaced a Roman frontier (limes) along the Stanegate guarded by a number of auxiliary forts, including Vindolanda.
Along the Wall there were 14 auxiliary forts, including Housesteads[?] and Birdoswald[?]. There were 80 fortlets with gates, known as Milecastles, one every Roman mile. Two turrets were set between each pair of Milecastles.
The Wall was part of a defensive system which included a glacis and ditch, the Wall itself, a military communications way and finally, on the south side, the Vallum, a ditch with two banks. The Vallum probably delineated a military zone rather than intending to be a major fortification.
A similar turf fortification, the Antonine Wall, runs between the Clyde and Forth estuaries in Scotland. As well as being less sophisticated, it was occupied and then reoccupied for a far shorter period as a decrease in the British garrison forced the Romans to fall back to Hadrian's Wall.