The foundations of Hadrian's ten-foot wide Wall were laid from Newcastle-upon-Tyne eastward for 23 Roman miles to Chesters in Northumberland, after that, apart from a few short lengths further west, the wall is reduced to eight or sometimes, six feet in width. We can assume that at some time during the early construction of the Wall, a decision was made to reduce its width, probably in order to speed-up the work.
The wall to the west of the River Irthing was originally built out of turf about sixteen feet wide, topped by a wooden palisade and walkway and punctuated by timber-framed turrets and milecastles. This 'turf-wall' was not long to endure, and section by section, it was all replaced in stone within a few years. It is thought that the reason why the western part of the Wall was built of turf was because there are no ready supplies of stone or lime near to hand along the western stretch, and at a later date it was decided to replace this with a regular stone wall. An alternative suggestion is that the turf-wall was temporarily substituted in order to speedily complete the barrier, possibly due to unrest among the tribes to either side, and was intended all-along to be replaced at a more leisurely pace later on, when arrangements had been made to quarry and transport the required stone.
The Wall Garrison
A Typical Milecastle
Small forts were built every Roman mile (1,620 yards) along the Wall for its entire length, and have for this reason been termed 'Milecastles'; the 80th milecastle at Bowness-on-Solway marked the western terminus of the Wall. The milecastles were made to a standard general pattern, built flush with the Wall on the north side, communicating with the rampart walk, and projecting to the south. They had two sets of large gateways one in the centre of the Wall face, and another in the middle of the southern wall. The superstructure of the northernmost of these two gateways was probably raised a further 10 feet above the level of the Wall rampart-walk, and surmounted by a raised fighting platform edged with a crenulated parapet. Most of the milecastles had their gateways partly blocked at a later date, which probably indicates that they were no longer used as access points through the wall.
The interior structures in each milecastle seem to have varied, but all contain at least one recognizable barrack-block. They housed a varying number of men with a conjectured maximum of about 64 soldiers, and were effectively large gate-houses, whose garrison were used originally to control egress through the Wall, and perhaps to levy a tax on goods carried through. Part of the garrison was certainly required to patrol the Wall rampart-walk, and possibly also to man the turrets along the Wall to either side.
Typical Turret Plan
Between each milecastle and the next were two smaller turrets, equidistant from each other and the milecastles to either side, with an average spacing of 540 yards between centres. They were of a uniform pattern, about 20 feet square, recessed into the Wall and built-up above the height of the Wall rampart walk. They apparently had no battlements and were roofed over with tiles. They housed a small garrison, possibly of eight men, four of whom would be on constant patrol duty along the Wall to either side. They were on two levels, with cooking facilities provided on the ground floor and sleeping quarters above, on a timber floor built level with the rampart-walk and accessed from below though a trap-door via a removeable ladder.
Turret Profile
In the original plan the Wall was to be garrisoned and patrolled from the Milecastles, and there was no requirement for any large forts to be built on the Wall itself. The wall was to be reinforced when needed, from the forts already in existence along the Stanegate, the old military highway from Corbridge to Carlisle built during the campaigns of governor Gnaeus Julius Agricola c.AD78, which ran to the rear of the wall an average three miles distant.
This format was to prove inadequate, however, and the wall was soon modified by the inclusion of several auxiliary forts along its length. These garrison forts were of a standard 'playing-card' profile, but varied in size between 3 and 5½ acres, depending on the type of unit it was built to house. In the infantry forts, the Wall itself generally formed the northern defences of the camp, which projected wholly to the south, as is the case with the Milecastles and turrets. In the cavalry forts, or those of part-mounted units, the forts were generally built across the line of the Wall with three of its major gates opening out onto its northern side, part of the wall having to be demolished in order to accomodate the fort. In some cases forts were sited on top of milecastles, which also had to be demolished, as at Bowness on Solway.
The Vallum
Shortly after work on the Wall had been completed a large earthwork was constructed, which followed along almost the full length of the Wall a short distance to the south. This earthwork, known as the vallum, consisted of a continuous steep-sided trench, ten feet deep and twenty feet across with a flat-bottom, unlike the ditch fronting the Wall which had a normal Roman military V-shaped profile. A twenty-foot wide turf bank about ten feet high was erected to either side of the ditch, which ran centrally between the two banks and was separated from them by a thirty foot wide space or berm. The overall dimensions of the entire construct was 120 feet.
Section Through The Vallum
The vallum followed close behind the Wall for almost its entire length, being conspicuously absent in the stretch from Wallsend from Newcastle, but running uninterrupted from the bridge over the River Tyne to the large auxiliary fort at Bowness on the Solway Firth. Were it not overshadowed by the close proximity of Hadrian's Wall, the vallum would itself be a frontier earthwork worthy of note.
At the points where it passed the forts and milecastles on the Wall, the vallum ditch was left uncut and there was a corresponding gap in both banks, forming a causeway which carried the road issuing from the porta decumana (rear gate) of the fortification.
In its eastern section the vallum runs an almost regulatory sixty feet from the Wall, except for short sections near Mile Castles 8 and 14, and a two-mile stretch between MC.15 and MC.17, where it lies almost ¼mile away from the Wall; in all these cases where the vallum departs from the line of the Wall it is in order to take a more direct line. The vallum and Wall part company at Mile Castle 33, where the rampart and wall-walk beetle along the edge of Sewingshields Crags, Hotbank Crags, Steel Rigg and Winshields Crags, while the vallum takes the more sedate route, often over ½ mile away along the southern slopes.
The Wall and vallum greet each other briefly near Great Chesters and re-unite again at Carvoran at the opposite end of the Peatsteel Crags, thereafter, the two linear barriers run almost parallel all the way to Stanwix, departing company only for a short stretch at Castlesteads. Beyond the large cavalry fort at Stanwix, the vallum proceeds westwards to the Bowness terminus with only three or four relatively minor re-alignments, and mostly ignores the tooth-like, meandering course of the Wall in this region.
It is thought that the vallum was intended to mark-out a kind of rearward boundary or "exclusion zone" behind the Wall, as it was not topped by either a palisade or a rampart walk. If this was its function, why did the it have to be built on such a monumental scale, where a simple palisade or ditch would have sufficed, and would have been many times more cost-effective?
Another school of thought is that its main purpose was as a communication route, with perhaps the northern side used for military traffic and the southern for civilian. The thirty foot wide berms certainly could have served as roadways, and the ten-foot high mounds would have provided ample cover for the deployment of cavalry along the rear of the Wall. The 'cavalry runway' idea should be rejected, however, as the dead-straight lines of this enigmatic earthwork, which pays no account to the steepness of terrain over which it passes, is not really suitable as a communication route, and no remains of a metalled road surface have been recorded.
An idea recently expounded, is that the vallum served no other purpose than to punctuate the northern frontier of Rome, and was deliberately built on a monumental scale on the orders of emperor Hadrian, who certainly did nothing by half-measures. Whatever function the vallum served appears to have been only temporary, however, because after being in use for only about a decade, the two mounds were slighted and thrown into the central trench at points spaced every 45 yards or so along its entire length.
The Roman Military Way
At first, the Wall garrison was supplied along roads which issued from the Decuman Gates at the rear of each fort and connected to the Stanegate, which ran parallel with the Wall a mean 2½ miles to the south. These supply-roads were provided to each of the main forts on the Wall, and also to a few of the milecastles, but many of the milecastles and nearly all of the turrets had to be supplied along tracks and trails along the line of the Wall.
At about the same time as the vallum was decommissioned c.AD140, the Wall was provided with its own purpose-built, metalled supply road which ran between the Wall and the vallum - lending some little credence to the theory that the vallum once served in this capacity. This new road connected each of the garrisons on the Wall, and ran through the rear portion of each fort, along the via quintana, passing through small gateways in the defences on either side. An exception to this rule is at Vercovicium (Housesteads) where the fort actually faces east, and the Military Way therefore passes along the main axis of fortification, through its Praetorian and Decuman gates.
In addition to providing a shorter and more secure route between each fort, there were branch-roads serving the milecastles, and pathways to all of the turrets probably branched-off from it. The modern name for this road is the Roman Military Way
