Sunday, 13 December 2015

Gorgan Wall Marine Geophysical Survey 2015

Hunting the drowned “Red Snake” – The Sasanian Persian Empire’s Great Walls

 One more field site for the year - at least I think so!  A couple of years ago Prof. Eberhard Sauer (Edinburgh University) got in touch as he has had a 10yr project investigating the “Red Snake” of Persia.  This is better known as the Gorgan Wall that once ran near the border of Iran and Turkmenistan from the Caspian Sea in the west and the Elburz Mountains in the east.
At a known length of over 195km it was pretty significant as an ancient line of defense.  However, not so today as the westernmost part not visible even to archaeologist in the present landscape. The problem with the wall is that it was constructed of mud bricks and so the ravages of time and the deconstruction (robbing) of bricks for use means that it is often difficult to see today.  However there is a silver lining, or at least a geophysical signature silver lining, that results from the use of bricks.  That is that the firing process of making bricks can give a strong magnetic signature to the bricks.   To make them requires a few key ingredients, namely a good clay with some larger silt or sand grains and water.  Lucking the clay is in abundance all along the wall’s path but water in this semi-arid area can be a problem.  So a solution was found by diverting local rivers to run feeder canals to a ditch that ran along the length of the wall thus providing not only the vital water but at the same time a quarry for the clay and when the wall was completed an extra defense line!
C5-6th   Kiln 
195km of wall requires quite a few bricks – it has been estimated that over 200 million in total were used!  Making these bricks was achieved using temporary field kilns set up all along the path of the wall at approximately 50m intervals.  The wall was garrisoned by an arm of over 20,000 soldiers barracked in at least 30 forts. The project team have spent the last few years excavating some of these kilns together with some of the forts and sections of the wall itself.  They have also investigated a sister wall, the Tammisheh Wall that ran from the southeast corner of the Caspian south to the Elburz Mountains.  Through C14 and OSL (Optically Simulated Luminesance) dating their work puts a construction date on both walls to the Sasanian Persian Empire between the 5th and 6th Century AD.

So what am I doing here?  The western extent of both walls is unknown.  Historical writing describes how the walls enter the Caspian Sea and certainly the Tammisheh Wall can be traced almost to the modern shoreline but where it goes after that is unknown.  Some descriptions even suggest that both walls were joined up. So we are back again to our old problem of changing sea levels and with it the usual battering that this can give to the landscape and our human endeavours. 

So I am here to help out with the searching for the walls, both on the sea floor and beneath it if they have been covered by more recent sediments.  We were looking for upstanding bricks or a scattering of bricks on the seafloor with the hope they would not have disintegrated.  Beneath the seafloor the hope was again to find lines of bricks or mounds.  Perhaps we would also see the cross –section of the trench that ran along the wall.  With the magnetic signature associated with the kilns on land this might stand out too but for this first preliminary survey I chose to use the Tritech Seaking Parametric Sub-bottom Sonar that we have found so effective in the shallow waters of Orkney together with an ultrahigh resolution Tritech Starfish 990kHz Sidescan Sonar. A great advantage of both these systems is that they can be taken as hand luggage on flights!
small boat work with Tritech Sub-bottom sonar and Starfish Sidescan
We started with the Tammisheh Wall as the projection into the Caspian is better known. The parametric sonar proved worthwhile once again despite the occasional gas blanking by picking out a strong reflection from the brick scatter on the sea floor.  The signature of this continued as it became buried further offshore with up to 2m of sediment.  After approximately 3km it abruptly disappeared or terminated.  The scatter on the sea floor was also mapped with the sidescan sonars from which the surface brick scatter was readily identified together with a number of linear features.

Given the time available for this trip and the relatively less knowledge on where the Gorgan Wall might be crossing the shore line we had a much larger potential target area to cover.  With a few days of poor weather (yes the Caspian does get rough with over a 1m wave and swell heights) we covered a large area but without finding any definitive wall signatures.  So more and better targeted data acquisition is needed for the marine side here.  What I now propose is to return and try with a magnetometer and an electromagnetic ground conductivity meter to survey from the last known western point of the wall across the land and shallow lagoons to the shore.  If we can trace this then we stand a much better chance of mapping it offshore, if that is where it goes. Video summary of the trip:

I had a fantastic crew out with me on the water (I cannot thank Hamid, Bardia and Hassan enough) and also back in the base as the joint project leaders, Dr Jebrael Nokandeh of the National Museum of Iran and Eberhard have assembled a talented team of archaeologists for the project.
So, another privileged trip to work with some great people, such friendly banter, engaging conversation, fantastic archaeological potential, some great food and wonderful scenery – the bird life on the Caspian is stunning!  I can’t wait to return next summer equipped with magnetometers and electromagnetic gear to continue the hunt.

Iran-British Gorgan Wall Project Team
Dr Jebrael Nokandeh (National Museum of Iran); Mr Hamid Omrani Rekavandi (Iranian Cultural Heritage, Handcraft and Tourism Organisation of Golestan Province); Bardia Shabani, Hassan Taji, Mohammad Ershadi, Maryam Hosseinzadeh, Mohadeseh Mansouri, Meghdad Mirmousavi, Mohammad Bagher Bayati Mehdi Jahed, Alireza Salari, Esmaeil Safari Tamak, Majid Mahmudi, 


  1. After 60 hard working days nothing could make us happier than Dr.Richard Bates Marine Geophysical Survey results, thanks to his invaluable knowledge and experience which provided a promising future to the Gorgan Wall project.

    Looking forward to meet him once again here in Iran