If you want to know more about Hadrian's Wall than the brief outline you will get from a guide book, then this scholarly piece of work is what you need. It is a very detailed account of the functions, structure, history and development of the wall, as well as of what life was like along the wall in Roman times.
The Emperor Hadrian ordered the building of the wall in A.D. 122. What was the purpose of such an undertaking? First of all Breeze and Dobson show what the wall was NOT. It was not a defensive structure for fighting from, in the way that medieval city walls were. It was not for Roman soldiers to stand on top of, behind the battlements, fighting off besieging invaders from the north. Roman military strength lay in fighting battles in the open. If there was any trouble from the tribes to the north, the Romans would meet it by sending out troops from the forts on the wall.
An ancient biography of Hadrian states that he built the wall "to separate the Romans from the barbarians". This gives us a better idea of its purpose. It was essentially a frontier. It was built to provide border control. It controlled (and taxed) the movement of people across the border of the Empire.
The wall also provided security. It might only be a hindrance to large-scale attacks, which would be met on open ground, but it would prevent petty raiding. Its milecastles and turrets would also be look-out points. And its very existence would be a form of control, over people to the south as well as the north. The fact that a ditch-and-mound system, the Vallum, was built parallel to the wall on the south side, shows that the people on that side had to be controlled, too.
Above all, according to Breeze and Dobson, the wall signified the "concept" of a frontier. This was a new idea for the Romans at that time. In the preceding centuries Rome had been constantly expanding. It had been assumed that this expansion would go on and on.
But now the Empire was reaching its limits. Expansion was no longer so easy. In the East there was the Parthian Empire, which was a tough nut to crack. Elsewhere Rome had reached what historian Neil Faulkner calls the "plough line", beyond which expansion would not pay for itself because the land was not fertile enough to produce much of a surplus. Hadrian ordered the building of frontier barriers in various parts of the Empire, including Germany, where it consisted of a timber palisade, and North Africa. Hadrian's Wall is simply the best known, best preserved and most impressive of these barriers.
Expansion did not come to a complete end with the building of the wall. For example, the frontier was for a short time moved northwards to the Antonine Wall; and the Emperor Septimius Severus later made an unsuccessful attempt to conquer the whole of Britain. Nevertheless the wall does signify a new stage in the development of the Roman Empire. And from this point of view it can be seen as a sign of weakness rather than strength.
In his magnificent book, "The Class Struggle in the Ancient Greek World", G.E.M. de Ste. Croix argues that the end of Rome's expansion led eventually to its decline. Conquered provinces were a source of taxation in cash and kind. But they were also a source of slaves, especially during the process of conquest itself. But when expansion ceased, the supply of slaves began to dry up. To make up for this, Rome's rulers began to squeeze the free peasants more and more, to the point where many peasants preferred "barbarian" invaders to Roman rule.
All this suggests that Hadrian's Wall symbolises a turning point in Roman history. Although its building was followed by a long period of continuing Roman power, the pinnacle had been reached. There was nowhere else to go but backwards.
Hadrian's Wall is an impressive monument to Roman power and engineering. To us, its remains also look beautiful: they run through wonderful scenery and form what guide books might call a "romantic ruin". But eighteen hundred years ago it would not have been seen as "beautiful". Impressive and awe-inspiring, yes; but not beautiful. In fact to the majority of the native population it would have been a symbol of oppression which was occasionally fought against and the rest of the time sullenly resented.