Hadrian's Wall: Encyclopedia II - Hadrian's Wall - Construction

Hadrian's Wall - Construction

Construction started in 122 and was largely completed within ten years, with soldiers from all three of the occupying Roman legions participating in the work. The route chosen largely paralleled the nearby Stanegate road from Carlisle to Corbridge, which was already defended by a limes and several auxiliary forts, including Vindolanda.

The initial plan called for a ditch and wall with 80 small, gated milecastle forts every Roman mile holding a few dozen troops each, and pairs of intermediate turrets used for observation and signalling. The wall was initially designed to a width of 3 metres (the so-called "Broad Wall"). The height is estimated to have been around 5 or 6 metres. Local limestone was used in the construction, except for the section to the west of Irthing where turf was used instead as there were no useful outcrops nearby. The turf wall was 6 metres wide and around 3.5m high. Milecastles in this area were also built from timber and earth rather than stone.

The milecastles were of three different designs, depending on which Roman legion built them — the Second, Sixth, and Twentieth Legions, whose inscriptions tell us were all involved in the construction. Similarly there are three different turret designs along the route. All were about 493m apart and measured 4.27m square internally.

Construction was divided into lengths of about 5 miles. One group of each legion would create the foundations and build the milecastles and turrets and then other cohorts would follow, building the wall itself. Early in its construction the width of the wall was narrowed to 2.5 metres or even less (the "Narrow Wall"). The Broad Wall dimensions can be seen in some stretches of foundations and some milecastle walls — a handy reference for archaeologists trying to piece together the construction chronology.

Within a few years it was decided to add a total of 14 full-sized forts along the length of the wall, including Housesteads and Birdoswald, each holding between 500 and 1000 auxiliary troops (no legions were posted to the wall). The eastern end of the wall was extended further east from Pons Aelius (Newcastle) to Wallsend on the Tyne estuary. Some of the larger forts along the wall, such as Chesters and Housesteads, were built on top of the footings of milecastles or turrets, showing the change of plan. An inscription mentioning early governor Aulus Platorius Nepos indicates that the change of plans took place early on. Also some time still during Hadrian's reign (i.e., before 138 AD) the wall west of the Irthing was rebuilt in sandstone to basically the same dimensions as the limestone section to the east.

After the forts had been added (or possibly at the same time), the so-called Vallum was built on the southern side. It consisted of a large, flat-bottomed ditch 6m wide at the top and 3m deep bounded by a berm on each side 10m wide. Beyond the berms were earth banks 6m wide and 2m high. Causeways crossed the ditch at regular intervals. Initially the berm appears to have been the main route for transportation along the wall. The Vallum probably delineated a military zone rather than intending to be a major fortification, though the British tribes to the south were also sometimes a military problem.

The Wall was thus part of a defensive system which, from north to south included:

• a glacis and a deep ditch armed with rows of pointed stakes
• the Wall itself
• a later military road (the "Military Way")
• the Vallum — two huge banks with a ditch between.

Adapted from the Wikipedia article "Construction", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki