Hadrian's Wall (Latin: perhaps Vallum Aelium, "the Aelian wall") is a stone and turf fortification built by the Roman Empire across the width of what is now northern England. Begun in AD 122, during the rule of emperor Hadrian, it was the third of four such fortifications built across Great Britain, the first being from the River Clyde to the River Forth under Agricola and the last the Antonine Wall. All were built to prevent military raids on Roman Britain by the Pictish tribes (ancient inhabitants of Scotland) to the north, to improve economic stability and provide peaceful conditions in Britain, and to mark physically the frontier of the Empire. Hadrian's Wall is the best known of the three because its physical presence remains most evident today.

The wall marked the northern limes in Britain and also the most heavily fortified border in the Empire. In addition to its use as a military fortification, it is thought that the gates through the wall would also have served as customs posts to allow trade taxation.

A significant portion of the wall still exists, particularly the mid-section, and for much of its length the wall can be followed on foot. It is the most popular tourist attraction in Northern England, where it is often known simply as the Roman Wall. It was made a UNESCO World Heritage Site in 1987. English Heritage, a government organization in charge of managing the historic environment of England, describes it as "the most important monument built by the Romans in Britain".[1]

Dimensions

Sections of Hadrian's Wall remain near Greenhead and along the route, though other large sections have been dismantled over the years to use the stones for various nearby construction projects.

Hadrian's Wall was 80 Roman miles (73.5 statute miles or 117 kilometres) long[2], its width and height dependent on the construction materials which were available nearby. East of River Irthing the wall was made from squared stone and measured 3 metres (9.7 ft) wide and five to six metres (16–20 ft) high, while west of the river the wall was made from turf and measured 6 metres (20 ft) wide and 3.5 metres (11.5 ft) high. This does not include the wall's ditches, berms, and forts. The central section measured eight Roman feet wide (7.8 ft or 2.4 m) on a 10-foot (3.0 m) base. Some parts of this section of the wall survive to a height of 10 feet (3.0 m).

Route

Map showing the location of Hadrian's Wall

Hadrian's wall near Housesteads

Hadrian's Wall extended west from Segedunum at Wallsend on the River Tyne to the shore of the Solway Firth. The A69 and B6318 roads follow the course of the wall as it starts in Newcastle upon Tyne to Carlisle, then on round the northern coast of Cumbria. The wall is entirely in England and south of the border with Scotland by 15 kilometres (9 mi) in the west and 110 kilometres (68 mi) in the east.

Hadrian

Hadrian's Wall was built following a visit by Roman Emperor Hadrian (AD 76–138) in AD 122. Hadrian was experiencing military difficulties in Roman Britain and from the peoples of various conquered lands across the Empire, including Egypt, Judea, Libya, Mauretania, and many of the peoples conquered by his predecessor Trajan, so he was keen to impose order. However the construction of such an impressive wall was probably also a symbol of Roman power, both in occupied Britain and in Rome.

Frontiers in the early empire were largely based on natural features or fortified zones with a heavy military presence. Military roads often marked the border, with forts and signal towers spread along them, and it was not until the reign of Domitian that the first solid frontier was constructed, in Germania Superior, using a simple fence. Hadrian expanded this idea, redesigning the German border by ordering a continuous timber palisade supported by forts behind it. Although such defences would not have held back any concerted invasion effort, they did physically mark the edge of Roman territory and went some way to providing a degree of control over who crossed the border and where.

Hadrian reduced Roman military presence in the territory of the Brigantes, who lived between the rivers Tyne and Humber, and concentrated on building a more solid linear fortification to the north of them. This was intended to replace the Stanegate road which is generally thought to have served as the limes (the boundary of the Roman Empire) until then.

Construction

Construction probably started in AD 122 and was largely completed within six years.[3] Construction started in the east 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), which was already defended by a system of forts, including Vindolanda. The wall in the east follows the outcrop of a hard, resistant igneous diabase rock escarpment, known as the Whin Sill. The wall incorporated Agricola's Ditch.[4] The wall was constructed primarily to prevent entrance by small bands of raiders or unwanted immigration from the north, not as a fighting line for a major invasion according to Johnson.[5]

The initial plan called for a ditch and wall with eighty 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. 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.

Roman fort at Corstopitum.

The milecastles and turrets were of three different designs, depending on which Roman legion built them — inscriptions of the Second, Sixth, and Twentieth Legions, tell us 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 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.

Early in its construction, just after reaching the North Tyne, the width of the wall was narrowed to 2.5 metres (8.2 ft) or even less (sometimes 1.8 metres) (the "Narrow Wall"). However, Broad Wall foundations had already been laid as far as the River Irthing, where the Turf Wall began, demonstrating that construction worked from east to west. Many turrets and milecastles were optimistically provided with stub 'wing walls' in preparation for joining to the Broad Wall, offering 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 to 17 (sources disagree) full-sized forts along the length of the wall, including Vercovicium (Housesteads) and Banna (Birdoswald), each holding between 500 and 1,000 auxiliary troops (no legions were posted to the wall). The eastern end of the wall was extended further east from Pons Aelius (Newcastle) to Segedunum (Wallsend) on the Tyne estuary. Some of the larger forts along the wall, such as Cilurnum (Chesters) and Vercovicium (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 (before AD 138) the wall west of the Irthing was rebuilt in sandstone to basically the same dimensions as the limestone section to the east.

Vallum at Hadrian's Wall near milecastle 42.

After the forts had been added (or possibly at the same time), the Vallum was built on the southern side. It consisted of a large, flat-bottomed ditch six metres (20 ft) wide at the top and three metres (10 ft) deep bounded by a berm on each side 10 metres (33 ft) wide. Beyond the berms were earth banks six metres (20 ft) wide and two metres (6.5 ft) high. Causeways crossed the ditch at regular intervals. Initially the berm appears to have been the main route for transportation along the wall.

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

• a glacis and a deep ditch
• a berm with rows of pits holding entanglements
• the curtain wall
• a later military road (the "Military Way")
• a north mound, a ditch and a south mound to prevent or slow down any raids from a rebelling southern tribe.

Garrison

The wall was garrisoned by auxiliary (non-legionary) units of the army (non-citizens). Their numbers fluctuated throughout the occupation but may have been around 9,000 strong in general, including infantry and cavalry. The new forts could hold garrisons of 500 men, while cavalry units of 1,000 troops were stationed at either end. The total number of soldiers manning the early wall was probably greater than 10,000.

They suffered serious attacks in 180, and especially between 196 and 197 when the garrison had been seriously weakened, following which major reconstruction had to be carried out under Septimius Severus. The region near the wall remained peaceful for most of the rest of the third century. It is thought that some in the garrison may have married and integrated into the local community throughout the years.

Part of Hadrian's wall near Housesteads.

After Hadrian

In the years after Hadrian's death in 138, the new emperor, Antoninus Pius essentially abandoned the wall, leaving it occupied in a support role, and began building a new wall in Scotland proper, about 160 kilometres (100 mi) north, called the Antonine Wall. This turf wall ran 40 Roman miles (about 37.8 mi (60.8 km)) and had significantly more forts than Hadrian's Wall. Antoninus was unable to conquer the northern tribes, so when Marcus Aurelius became emperor he abandoned the Antonine Wall and reoccupied Hadrian's Wall as the main defensive barrier in 164. The wall remained occupied by Roman troops until their withdrawal from Britain.