28 March, 2013

Hadrian's Ghost Wall

The key to understanding Hadrian’s Wall is that the Romans built a temporary frontier of wood in the East, and wood and earth in the West, to protect them while they constructed the permanent stone frontier. It follows that there would also be temporary forts and other structures amounting to a whole ghost timber and earth version of Hadrian’s Wall.

Understanding the Timber Wall.
The construction of a temporary Timber Wall is covered extensively elsewhere [eg; here / free download]  It explains and contextualises the rest of the evidence including;
  • The precise pattern position of the postholes found in several recent excavations. [1]
  •  How the Romans were able to build a stone wall and forts in potentially hostile territory over a number of years dispersed along a 73 mile /120 km front.
  •  The context of the Turf Wall
  •  The position, form, and course of the ditch
  •  The width of the berm  . . . Note;  Per Lineam Valli – Mike Bishop's excellent and detailed guide to remains of the Wall, did me the honour of mentioning my work in this context.
…a series of short stubby posts marking the position of a series of pits which we now know formed berm obstacles. These would have been filled with something like thorn bushes to form the Roman equivalent of a barbed-wire entanglement.
Wall Mile 0
The berm pits are not universally accepted as evidence of an entanglement. One writer has suggested that they are no such thing and in fact represent an early timber predecessor to Hadrian’s Wall. An interesting idea, but the absence of a berm between this putative timber wall and the ditch would make it unlikely on the grounds of stability,
It is important to deal with some of these misunderstandings.
  • The idea that the width of berm, wider than the Wall was tall, is for structural stability is an old but patently unfounded idea, inconsistent both with Roman practice elsewhere such as the Turf Wall, and a modern understanding of soil mechanics.
  •  Similarly, the idea that the large roughly circular postholes, up to 600 per 100m, could have held thorn trees with interlocking branches [2] is inconsistent with morphology of native trees and completely unrealistic in terms of arboriculture.  
  • These postholes have nothing to do with the branches and tree trunks buried in a backfilled ditch hundreds of feet from the Roman line [Cippi ] during the Siege of Alesia mentioned once by Caesar [3]. 
  • However, they fit perfectly with the building of timber ramparts with a ditch in front, mentioned Caesar on numerous occasions, described by other authors, and which might be regarded as standard practice for the Roman army.[4]
Rethinking the Wall
Once it is understood that this was a live military frontier, and the Roman army was in the field, I want to focus on two observations and follow them through;
  •  The Roman army always dug in using earth and timber [4]
  •  You cannot defend a stone fortification while it is under construction.
It follows;
  •  Therefore for every stone fort there must be a temporary timber and earth fort to house the work force and garrison.

A selection of medium sized camps near the Hadrian’s Wall on Google Earth

  • In addition, since the construction force was larger than the eventual garrison, temporary works may be more extensive than those of the finished frontier.
  •  Since gateways in forts and mile castles are the most technical aspects of the main Wall, the skilled legionary labour, working westwards, was probably spread out to mile castle level over quite long stretches simultaneously. [5]
  •  It would seem likely for the sake of logistics that there were smaller camps to house those garrisoning and building the sectors of wall between the main forts.

 A selection of small camps from behind the Wall in the central sector 

The Story so far 
  • After the first few seasons, a temporary frontier of earth and timber had been established, with fortifications housing the garrison of Auxiliaries as well and the legionaries, who working west, had built much of the "Broad" Stone Wall as far as the North Tyne.
  • The construction of the wall has reached the central sector, [the only section where both the stone and earth forts and Wall now survive].
The Dislocation
  • Some scholars now think it likely that work on the wall was disrupted, probably by War. [6]
  • When work resumed, probably after several years, the both quantity and quality of the work is scaled back.
  •  Then, almost as soon as the Wall is finished, it is abandoned in favour of a shorter more concentrated frontier further north. [The Antonine Wall].

Some of the larger Temporary camps near Hadrian’s Wall on Google Earth

So what might have happened?
When people see the central sector they ask the question who would attack the Wall up here?  Which is precisely the point, and perhaps not one lost on the Romans.
The central sector might be a good place to attack the Wall because;
  • The Stone Wall fortifications were not yet finished.
  •  There is good cover in rough uneven terrain to North of Wall.
  • Might catch a legionary force spread out in work details.
  •  The Region is furthest from the coast – from where reinforcements can be brought in by sea.
  •  Splits the Roman forces in half.
  • Hold the high ground in the centre with options to move south on either flank of the Pennines.
  • From the Roman point of view the forces along the frontier are now dispersed and facing the wrong way.
  •  The two land routes reinforcement can come from York or Chester, both can be out flanked by a force in the centre
  • It is also worth noting that the east central sector was reinforced with extra forts when work resumed after the dislocation,  [the fort at Carrawbrough/ Brocolitia below].
Notwithstanding this speculation, the central sector is the only place where the temporary camps cans be found,so these slight structures may preserve the best evidence of how work on the wall was organised and perhaps even what happened to so disrupt its progress.
While the stone fortifications may continue to be the focus of attention, we should not overlook that these less prominent and very fragile remains of the long Roman occupation of Northern England which  have yet to be systematically explored.  
If we are ever to understand the complex history and origins of Britain's largest ancient monument, the form and extent of these temporary works must be considered. 

Sources & further reading
Note; This article uses illustrations based on images from Google Earth: ttp://www.google.com/earth/index.html [Accessed 07/12/11]

[1]Bidwell, Paul T.; Watson, Moira. 1989 'A Trial Excavation on Hadrian's Wall at Buddle Street, Wallsend'. Archaeologia Aeliana, 5th ser., 17 (1989), 21-28.
T. Frain, J. McKelvey & P. Bidwell 2005 Excavations and watching brief along the berm of Hadrian’s Wall at Throckley, Newcastle upon Tyne, in 2001-2002. Arbeia J, 8 53-76.
Grey literature; Throckley, Newcastle upon Tyne, archaeological excavation and watching brief. TWM Archaeology 12/2003  TWM archaeology 10/2006
Grey literature: Shields Road, Newcastle, Phase 2b, archaeological excavation.
Grey literature: Newcastle, Melbourne Street, Archaeological excavations. Archaeological services, University of Durham. http://csweb.bournemouth.ac.uk/aip/gaz2004/ene.pdf
 [2] Bidwell, P T, 2005 'The system of obstacles on Hadrian's Wall; their extent, date and purpose', Arbeia J, 8, 53-76. http://www.arbeiasociety.org.uk/journal.htm
 [3] Caius Julius Caesar De Bello Gallico VII.73  [De Bello Gallico and Other Commentaries English translation by W. A. MacDevitt, introduction by Thomas De Quincey (1915) http://www.gutenberg.org/etext/10657]
 [4] In addition to Caesar [op cit.] see also; The Military Institutions of the Romans (De Re Militari) by Flavius Vegetius Renatus, Translated from the Latin by Lieutenant John Clarke, translation published in 1767.   [Etext version by Mads Brevik (2001) http://www.pvv.ntnu.no/~madsb/home/war/vegetius/]
And Polybius; http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Polybius/18*.html#18 [Accessed 25/03/2011],
[5] Hill, P. R. 2006. The construction of Hadrian's Wall. Tempus, 
[6] [Opt cit.]Chapter 10 and Breeze, D.J. 2003. "Warfare in Britain and the Building of Hadrian's Wall." Archaeologia Aeliana 32, 13 –16.


dustbubble said...

I must admit I'd be very unhappy with a wide berm in front of my timber wall. Ideal place to pile up furze and heather, and torch the thing.
And if there was one thing that the ancestors of the Caledonians were good at, it was roasting the bejasus out of fortifications, even stone timberlaced ones.
I'd rather have a nice wide soggy ditch.
Even if they did manage to fill it, it wouldn't get at the post socket/base level when lit and banked down to serious damaging heat.

Anyway, the timber wall should be pretty much self-bracing, without making heavy demands on the site, and not in need of elaborate foundations or substratum support like a humungous and fragile stone thing.

Geoff Carter said...

Good points - maintaining the berm, especially with 'obstacles', would be tricky and would soon turn into a hedge.
As an archaeologist you will know that the distance between the wall and the ditch, like any excavation, is governed by the angle of shear of the natural soil. The base of the foundation to the bottom of the ditch – distance of about 30’ -implies an angle of 11 degrees, - off the scale even for loose sand, never mind well compacted boulder clay.