Who built the Wall
The construction of the wall was the most elaborate project in the Roman world and was undertaken by the II Augustus, VI Victrix and XX Valeria Victrix legions. Detachments of the British fleet were used to build some of the forts granaries. The legions contained specialist skilled craftsmen such as engineers, stone masons and carpenters, while the general soldiers were also used to building. The Roman army also had it's own supply train of mules and oxen to help with the huge task of moving the building materials up to the Wall.
The entire project was without precedent, as before this time only relatively short city walls had been built out of stone. Even building city walls had fallen out of practice in the Roman world. While the Roman army did have experience of building forts, however these were made out of earth, or a stone face on an earth bank rather than a free standing stone wall.
Recent finds at Vindolanda have discovered the remains of a timber building with a large number of rooms, some of which would have been painted from this period. It seems likely that this may have been where Hadrian's party had been housed when he came to see the project. Vindolanda would have been a good site from where Hadrian could have watched the start of his project.
Hadrian's love of architecture
Hadrian had a huge interest in architecture and had a very high opinion of his own skills - Trajans brilliant architect Apollodorus was exiled on a mere pretext because he doubted Hadrians architectural abilities. Hadrian was especially interested in building on a colossal scale as shown by three of his other projects: Tivoli, his mausoleum which is now the Castel Sant Angelo in Rome and the Panthenon.
The Wall was therefore designed to be impressive. The turrets and milecastles regularly spaced, often with little concern shown to the topography of the land. The turrets in particular seem to meet a cosmetic as much as a practical purpose, it should come as no surprise that there's evidence that the wall was actually whitewashed.
Design of the Wall
The Wall was either 10 or 8 feet wide and probably about fifteen foot high. In the West the Wall was initially built in turf and only later rebuilt in stone. Every mile along the Wall was a fortlet (milecastle)with two regularly space towers between the milecastles. There were also two gateways for the main routes North of the Wall, these were for Dere street which crosses the Wall at Portgate just North of Corbridge, and just to the North of Carlisle - however little is known of their design. Just behind the Wall is the Vallum, a massive ditch, which would have originally been twenty feet wide and ten feet deep.
Later forts were moved up to the Wall. These were built roughly seven and a half miles apart, although the spacing is nowhere near as rigid as the milecastles (the distance varies from about six to nine miles), with the forts built near major river crossings. Where possible the forts have been built astride the Wall. It is thought that the Vallum was built at the same time as the forts were moved, although the Vallum obviously was designed to restrict access to the Wall from the South, it's exact purpose is unknown. It's size would make it a major monument in it's own right. Possible reasons that have been suggested for it include acting as a customs barrier or defending the Wall from the South.
The milecastles were about 60 by 50 Roman feet with Walls about 10 feet wide, the North side was the Wall itself. The milecastles usually contained one or two buildings, which were made from stone or timber and would have provided accomodation for perhaps a dozen men or less (the towers provide almost as much accomodation). They had a gate in the South side and to the North through the Wall, with the Northeern Gateway surmounted with a tower. The milecastles were built of stone (when the Wall was stone) and turf for those sections which had a turf Wall.
The towers were probably 30 foot high with the the top accessed by a ladder. The towers and milecastles may have given access to the Wall, although it whould be remembered that the top of the wall was NOT a fighting platform lined with soldiers repelling invaders. However it may have had a parapet allowing sentries to patrol the Wall.
As none of the Wall, towers or Milecastles survive to anywhere near their full height it's not really known what the top would have looked like. For example it's really only assumed that there was a parapet, it may have just been a Wall, similarly the design for the the top of the towers is not really known, with the assumption that they would have been similar to those shown on Trajan's column. The turret may have had flat or pitched roof.
The design had a number of changes during the construction of the Wall. The two most important of these was the change from Wide to Narrow gauge; that is from a ten foot width to an eight foot width. Presumably this was done to save time and effort building the Wall. The second was to move the forts up to the course of the Wall itself.
Originally the forts would have been located a few miles to the South of the Wall along the course of the Stanegate. This had the advantage of being much easier to supply than if the forts were along the Wall itself; however it also had the disadvantage of taking longer for the troops in the forts to reach the Wall itself. Moving the forts would have involved a major amount of extra work, including demolishing some of the turrets and milecastles already built. It can't have been a decision taken lightly and there must have been very good operational reasons for implementing it. At first the forts were built with three gateways facing North of the Wall, but in later forts this was reduced to one.
Completion of the Wall
The date when the Wall was finished is harder to say, the initial scheme probably took about three years, however the final work of rebuilding the turf wall in stone was completed only just before Hadrians death. The cost of the project would have been enormous even allowing for the fact that the army supplied the labor and the quarries belonged to the state. Indeed some believe that the fighting in Britain at the start of Hadrians reign was deliberately exaggerated to justify the scale of the project.
The Romans lack of experience in building such a monumental structure was to show through in a couple of ways:
i. A number of major redesigns were required during the building of the Wall, (For example the forts being moved up to the line of the wall).
ii. The construction was flawed - The Wall had been built with facing stones that were unusually long, with a front tapering to a point, this made them particularly prone to topple outwards. This meant it had to be rebuilt at the end of the second century by the Emperor Severus.
The rebuilding required was in fact so complete that until the start of the twentieth century it was believed that the Wall been built by Severus (and that Hadrian had only built the Vallum). Hadrian would have found this especially galling as he had a reputation as one of Rome's vainest emperors!
Hadrian died in AD 138 after a long illness. He had been one of Rome most capable and energetic emperors and had dedicated his life to the improvement of the state. He was a great patron of the arts and he ruled firmly and with the exception of his suppression of the Jewish revolt, humanely.