Hadrian Wall - Construction

Construction

Construction probably started sometime in 122 and was largely completed within six years. Construction started in the east, between milecastles four and seven, and proceeded westwards, with soldiers from all three of the occupying Roman legions participating in the work. The route chosen largely paralleled the nearby Stanegate road from Luguvalium (Carlisle) to Coria (Corbridge), upon which were situated a series of forts, including Vindolanda. The wall in the east follows a hard, resistant igneous diabase rock escarpment, known as the Whin Sill.

The initial plan called for a ditch and wall with 80 small gated milecastle fortlets, one placed every Roman mile, holding a few dozen troops each, and pairs of evenly spaced intermediate turrets used for observation and signalling. However, very few milecastles are actually situated at exact Roman mile divisions; they can be up to 200 yards east or west because of landscape features or to improve signalling to the Stanegate forts to the south. Local limestone was used in the construction, except for the section to the west of Irthing where turf was used instead, since there were no useful outcrops nearby. Milecastles in this area were also built from timber and earth rather than stone, but turrets were always made from stone. The Broad Wall was initially built with a clay-bonded rubble core and mortared dressed rubble facing stones, but this seems to have made it vulnerable to collapse, and repair with a mortared core was sometimes necessary.

The milecastles and turrets were of three different designs, depending on which Roman legion built them — inscriptions of the Second, Sixth, and Twentieth Legions, show that all were involved in the construction. All were about 493 metres (539 yards) apart and measured 4.27 square metres (46.0 square feet) internally.

Construction was divided into lengths of about 5 miles (8.0 km). One group of each legion would excavate the foundations and build the milecastles and turrets and then other cohorts would follow with the wall construction. It was finished in 128.