Hadrian's Wall (also called the Roman Wall, Picts' Wall, or Vallum Hadriani in Latin, was a defensive fortification in the Roman province of Britannia, begun in 122AD during the reign of the emperor Hadrian. It ran from the banks of the Tyne River near the North Sea to he Solway Firth on the Irish Sea. It had a stone base and a stone wall. There were milecastles with two turrets in between. There was a fort about every five Roman miles. From north to south, the wall comprised a ditch, wall, military way and vallum (another ditch with adjoining mounds). It is thought that the mileccastles were staffed with static garrisons, whereas the forts had fighting garrisons of infantry and cavalry. In addition to the wall's defensive military role, its gates may have been used as customs posts.
Hadrian's Wall was 80 Roman miles (73.0ml) long, its width and height varied according to the construction materials that were available nearby. East of the River Irthing, the wasll was made from squared stone and measured 3 metres (9.8 feet) wide and 5 to 6 metres (26-30 feet) high, while est of the river the was originally made from turf and measuted 6 metres (20 feet) wide and 3.5 metres (11 feet) high; it was later rebuilt in stone. These dimensions do not include the wall's ditches, berms and forts. The central section measured eight Roman feet wide (7.8ft or 2.4 m) and on a 3m (10ft) base. Some parts of this section of the wall still survive to a height of 3 metres (10 ft).
Immediately south of the wall, a large ditch was dug, with adjoining parallel mounds, one on either side. This is known as the Vallum, even though the word Vallum in Latin is the original of the English word wall and does not refer to a ditch. In many places - for example Limestone Corner - the Vallum is better preserved than the all, which has been robbed of much of its stone.
The purpose of construction: Hadrian's Wall was probably planned before Hadrian's visit to Britain in AD122. According to restored sandstone fragments found in Jarrow which date from 118 or 119. it was Hadrian's wish to keep "intact the empire", which had been imposed on him via "divine instruction". It is entirely possible that, on his arrival in Britain in 122, one of the stops on his itinerary was the northern frontier to inspect the progress of the building of the wall.
Although Hadrian's biographer wrote "Hadrian was the first to build a wall 80 miles long to separate the Romans from the barbarians". Reasons for the construction of the wall vary and no recording of an exact explanation survives. Theories have been presented by historians, mostly of an expression of Roman power and Hadrian's policy of defence before expansion. On his accession to the throne in 117, Hadrian had been experiencing rebellion in Roman Britain and from the people of various conquered lands across the Empire, including Egypt, Judea. Libya and Mauritania.
Hadrian's Wall was declared a World Heritage Site in 1987; it remains unguarded, enabling visitors to climb and stand on the wall although this is not encouraged as it would damage the historic structure. On 13 March, 2010, a public event illuminating the Wall took place, which saw the route of the wall lit with 500 beacons. On 31 August, and 2 September, 2012, there was a second illumination of the wall as a digital art installation called 'Connecting Light', which was part of the London 2012 Festival.
In 2003, a National Trail footpath was opened that follows the line of the wall from Wallsend to Bowness-on-Solway. Because of the fragile landscape walkers are asked to follow the path only in summer.
There is a lot more information on Wikipedia about the Wall but far too much to include here.