Construction: The wall was built by the three Roman Legions stationed in Britain, namely the II Augusta, the VI Victrix Pia Fidelis and the XX Valera Victrix legions from Caerleon, York, and Chester. Originally built in stone from the Tyne to the River Irthing and then as a turf embankment from there to the Solway, the turf wall was gradually replaced by stone with the entire length being stone by 163 AD.
Fortifications: At every mile along the wall are 'Milecastles' which housed approximately 60 men, and between each milecastle, two turrets at one third of a mile intervals. Along the wall were sixteen forts each housing between 500 and 1000 men. The wall was not garrisoned by the Roman Legions but by 'Auxiliary' troops - soldiers recruited from the conquered lands of the Empire.
The Ditch: An integral part of the Wall defences was the 'Ditch', a deep V-shaped excavation at the base of the north side of the wall. This was almost certainly dug at the time of building and runs the entire length of the wall except where it passes over the crags of the Whin Sil escarpment and along the Solway coast.
The Vallum: A later addition to the defences, the Vallum is a broader flat bottomed ditch with built up mounds on each side. Excavated some 60 to 80 yards to the south of the wall, it is likely that the Vallum defined a military zone between it and the wall. Around 160 to 180 AD, a military road was added within this zone.
History: Building began at Newcastle in 122 AD to a gauge of 10 feet. After approximately 27 miles the gauge was altered to 8 feet and at the same time the wall was extended in the east to Wallsend. In the west the wall was constructed in earth, and milecastles in earth and timber from the Solway to the River Irthing. East of the Irthing the wall was built to the 8ft gauge but on a foundation laid to the original 10 ft gauge. In 138 AD, following the death of Hadrian, the wall was largely abandoned as the new Emperor Antoninus Pius pushed north and constructed a turf wall from the Clyde to the Forth. This new 'Antonine' wall held for 20 years before the boundaries of the Empire were pushed back once again. Hadrian's Wall was re-occupied, renovated, and the last of the old turf and timber defences to the west of the River Irthing finally made stone. Hadrian's Wall then defined the Edge of Empire for a further 200 years until it was gradually abandoned as the Roman Empire in Britain collapsed between 380 and 410 AD.