I have just post this article in the board Britannia but in italian language

Introduction
The emperor Hadrian ascended to the throne in the 117 A.D. In the 122 A.D. he visited in Britain during a travel of inspection of the western provinces of the Empire. After taking stock of the military and political situation of the province, he ordered to the governor Pletorius Nepos, who had previously governed Germany Inferior, to construct a wall and a defensive ditch from Wallsend (on the mouth of the Tyne river) to Bowness on the Solway Firth (isthmus). This work of Roman military engineering is the largest and the greatest of the imperial period, as the siege-works of Alesia, constructed under the orders of Caius Iulius Caesar, had been for the republican period.
For approximately 300 years the wall of Caesar Hadrian Trajan Augustus (nomen of its gens is Aelia) was the north-west frontier of the Empire. It was replaced for approximately 22 years from the 138 A.D. to the 160 A.D. by the wall constructed by the emperor Antoninus d Pius 160 km further north. This wall ran between Forth and the isthmus of Clyde. Its length was 60 km (27 modern miles, about 40 roman miles)

SCOPE AND/OR OBJECTIVE the scope of this article is not the history of the wall from its construction until 407 A.D. when Emperor Constantinus III decided to abandon the province. It will instead concentrate on the physical aspects and its tactical and military implications.

FACT The three Roman legions who constructed the wall were those assigned to Britain: - II legion based at Caerleon (close to Newport, in the south of Wales);
- VI VICTRIX legion based in York;
- XX legio based in Chester.
The legions provided the architects, engineers, geometricians, topographers, carpenters and workers. All engineers belonged to the Corps of Engineers. They did not use slaves during construction, but it is possible to assume that the local civilians transported the materials.
Construction at lasted at least 6 years. Successive modifications werel be made after 138 A.D.

CHARACTERISTICS Of the WALL
The wall itself was fortified by a communication trench and merlato parapets. Each mile there was a watch tower. Between two consecutive towers, there were two merlate towers. In front to the wall the full of rocks land comes dug a pit except the places where natural terrain renders it superfluous. The material from the pit was piled to north in order to form another obstruction. Behind the wall there ran a road and a vallum with two lateral rises.
Here the main construction data:
- length of the wall 80 Roman miles (117 km) or 73 modern miles;
- the first 45 Roman miles (66.5 km) from Newcastle (British coast oriental) to the Irthing river are made of stone;
- the next 35 Roman miles (50.5 km) from the Irthing river to Solvay are made of blocks of tufo (turf);
- volume of the material of wall 1.670.000 m³;
MILECASTLES The wall has 81 castles (one for every mile). Each tower has two doors, one facing north and one towards south.
There were 2 turrets per tower giving 160 turrets for watching the north (every 2 castles). - height of the wall is 15. 6. (4.72 meters);
- height of the merlato parapet of the wall is 6. (1.52 meters);
- height of the wall more the parapet is 21. 6. (6.55 meters);
- width of the wall, constructed with stone or turf and inner filling of pietrisco (gravel?) 9. 6. (2.89 meters);

PIT (DITCH). Situated in along the northern side of the wall.
- it is of triangular shape and the bottom is shaped of parallelepipedo(?);
- length 117 km, 80 Roman miles, 72 modern miles;
- width 30. to the top (9.14 meters);
- depth 10. (3.04 meters);
- distance from wall 20. (6 meters);
- volume of the moved material 1.625.000 m³;

ROAD. The road Roman is long 73 modern miles long and is situated behind the wall. It was constructed later than the wall, but in the same century.
- hypothesis width 3 meters;
- depth 0.5 meters;
- volume of the moved material 175.000 m³;

VALLUM. Situated to south of the distant road and 60-100 yards from the wall.
- trapezioidale shape;
- depth 10. (3.04 meters);
- width at top 20. (6.08 meters);
- volume of moved material.

MOUNDS. They are two, one south and the other north of vallo.
- height 10. (3.048 meters);
- width approximately 20. (6.096 meters);
- distance between the two mounds and vallo the 30. (9.144 meters);
- volume of the material moved for mound 2.150.000 m³; - volume of the material moved for two mounds 4.300.000 m³;

The wall crosses three main rivers where they come constructed bridges in order to assure the continuity and the communications; the North Tyne, the Irthing and the Eden. A bridge called the pons Aelius probably was constructed to cross the Tyne at Newcastle.

TROOPS Initially it likely that the troops roomed in the blockhouses and the turrets were taken from the Roman units stationed behind the wall in Bretagna and Wales. There were 32 men assigned to each tower and therefore there were approximately 1,2880 men assigned to patrol the wall. In all the wall there are 81 towers and 160 watch turrets. Behind the wall there were regiments composed from unit of auxiliary type (heavy infantry, light infantry and cavalry) and several cohorts of 1,000 men of mixed infantry. Close to Carlishe, in the fort of Stanwix, there was an auxilliary unit of 1,000 knights. Its commander is officially the commander responsible for the wall, but he did not have authority over the commanders of the others cohorts or blockhouses stationed behind the wall. The regiments were placed in forts that were approximately 14 miles apart, about 1 day's march. There were 6 types of different regiments in size and type of troop members. These were auxilliary troops.
The most common type of regiment is composed from 500 men divided into heavy infantry, light infantry and cavalry. Legions were not stationed directly behind the wall but their absence was compensated for by the presence of cohorts of 1,000 men (larger than one normal cohort of 600 men). As well, these tactical units were supplied of mixed and vavalleria infantry (skirmishers?). They were probably formed from centuries of 80 men with a centurion in charge. The cavalry was arranged in groups of 32 men and with a decurion in charge. (?)

FUNCTIONS Of the Wall
- control of the frontiers. Access to imperial territory Roman was only allowed to peopel from the other side of the wall for commercial reasons;
- to stop the continuous attacks of the barbarian Caledoni and the armed bandits across the territories of the frontier. The soldiers who manned the wall only watched the northern frontier, they were not expected to counterattack a large number of screaming blue Picts. Their numbers and armament would not have allowed them to repel a determined attack right along the wall.

NOTES To south of the wall we have strong following: Bowness on Solway, Burgh, Castlesteads, Carvoran, Great chesters, Halton chesters, Rudchester, Stanwick, Carrawburgh, Birdoswald, Housesteds, Chesters, Benwell, Vindolandia/Chesterholm. To north of the wall we have strong following: Bewcastle, Netherby, Birrens the following Troviamo then bridges: the Chester bridge Abutment and the Willowford bridge Abutment. JOINED. OF MEASURE ROMAN 1 pes (foot) = 11.6 inches = 29.5 centimeters 1 passus (step) = 5 pedes (feet) = 1,61 yd =