Detection and Documentation of the Great Wall of Gorgan

by Dr. Abbass Malian

The Great Wall of Gorgan or the Red Snake (which owes its name to its red color bricks), is a historical wall that extends from the Caspian Sea to the top of the Alborz Mountains. Almost all of this wall is now gone, leaving only small parts of it buried underground. The Great Wall of Gorgan, with a length of about 200 km, the construction of which took more than 90 years, is the longest historical monument in Iran and the largest defensive wall in the world after the Great Wall of China. The historical wall of Gorgan dates back to the Sassanid period. Archaeologists have dated it to the 5th century AD.

Situation of the Great Wall

The Persian kings built this awesome and sophisticated barrier against the attacks of the central Asia nomad tribes or as the holy books says: “A wall against the enemies of God”.
This historical wall, along with ditches, brick kilns, dams, and water supply canals, forts attached to the wall and fortresses around it, is a magnificent and unique cultural heritage entity. Detection and documentation of the Great Wall of Gorgan are being prepared for inclusion in the World Heritage List of the United Nations Educational, Scientific and Cultural Organization (UNESCO).

Oblique color photo of the remains of the Great Wall

Archaeological excavation on the remains of the Great Wall

Remote sensing and photogrammetry methods were employed in order to detect and document the Great Wall of Gorgan, respectively.
In the first part of the documentation project, historic aerial and satellite imagery including CORONA images were used for detecting and positioning of the hidden or damaged parts of the Great Wall. Based on the results of the first part, the geometrical and spectral characteristics of this huge monument were documented in the second phase of the project by means of modern HR satellite images and UAV photogrammetry.
In this project, the efficiency of modern photogrammetric and remote sensing techniques for change detection and documentation of the Great Wall of Gorgan was explored. For this purpose, different types of aerial and spatial images were fused and prepared with appropriate spatial, spectral, and temporal resolutions, and were subjected to proper processing, in order to track the promising signals around the Great Wall.

Old aerial photo of the Great Wall region (1955)

IKONOS image of the Great Wall near Gonbad city (2000)

CartoSat satellite image of the Great Wall region (2011)

Corona photo of the Great Wall (1967)

In this line, both spectral and structural characteristics of ancient features together with the fusion of different level images were used to make appropriate data to be used in decision making for detecting the desired monument using Fuzzy ANP method. The layers were then combined based on an overlaying method to get the best probable output, i.e. the map of promising areas of the ancient remains of the Red Snake. The result is fully consistent with the facts so far discovered in situ.

As for the documentation of the detected features, precise photogrammetric reconstruction and 3D modeling of the monument and its surroundings were accomplished by means of a quadcopter UAV. High-quality ground control network was established using a global navigation satellite system (GNSS) so as to provide absolute orientation as well as a checking measure of the accuracy of the operation.

This project was carried out based on a research contract No. 1-755/140/952 between Shahid Rajaee Teacher Training University and the Ministry of Cultural Heritage, Golestan province. The project manager was Dr. Abbass Malian and the main colleagues were Ms. Somayeh Aslani Katooli, Mr. Mahdi Karimi, and Mr. Hamid Omrani Rekavandi.

Spectral index maps produced: 1) Lime detection band ratio, 2) Iron-oxide detection band ratio, 3) NDVI, 4) NDSI, 5) Clay detection band ratio, 6) NDWI

a) slope map b) aspect map

3D digital model of the Great Wall area

Contribution of each criterion in the final decision according to the assigned weights

UAV Operation / GNSS Operation


  1. Detection of Buffer Changes of Historical Monuments and Sites using Remote Sensing Methods (Case Study: Great Wall of Gorgan), Abbass Malian & Seyyed Ahmad Hosseini Fathabad, EARSeL 3rd International Conference on Advances in Remote Sensing for Archaeology and Cultural Heritage Management, University of Ghent, Belgium, DOI: 13140/2.1.4695.2641, 2012.
  2. Technical Report : Documentation and Detection of the Great Wall of Gorgan (in Persian), Abbass Malian, Ministry of Cultural Heritage, Golestan Province, Research Contract, No. 972-140-1-755, 2019.
  3. Linear Barriers of Northern Iran: The Great Wall of Gorgan and the Wall of Tammishe,Jebrael Nokandeh, Eberhard W. Sauer, Hamid Omrani Rekavandi, Tony Wilkinson, Ghorban Ali Abbasi, Jean-Luc Schweninger, Majid Mahmoudi, David Parker, Morteza Fattahi, Lucian Stephen Usher-Wilson, Mohammad Ershadi, James Ratcliffe & Rowena Gale, Iran, 44, No. 1, pp. 121-173, DOI: 10.1080/05786967.2006.11834684, 2006.
  4. Remote Sensing: An Advanced and Efficient Tool for detection and Documentation of the Greatest Historical Monument of Iran (in Persian), Somayeh Aslani, Abbass Malian, Jamaleddin MahdiNejad & Hamid Omrani Rekavandi, 1st National Conference on the Documentation of Natural & Cultural Heritage, Shahid Rajaee Teacher Training University, Tehran, 2018.
  5. Hunting the Red Snake (in Persian), Somaye Aslani, Abbass Malian & Saeed Sadeghian, 24th National Geomatic Conference, National Cartographic Center (NCC), Tehran, Iran, 2017.
  6. Detection and Documentation of Surface and Sub-Surface Cultural Heritage by Means of Remote Sensing (in Persian), Somayeh Aslani, M.Sc. Thesis, Supervisor: Dr. Abbass Malian, Department of Geomatics, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, 2017.
  7. An Imperial Frontier of the Sasanian Empire: Further Fieldwork at the Great Wall of Gorgan,Hamid Omrani Rekavandi, Eberhard W. Sauer, Tony Wilkinson, Esmail Safari Tamak, Roger Ainslie, Majid Mahmoudi, Seren Griffiths, Mohammad Ershadi, Julian Jansen Van Rensburg, Morteza Fattahi, James Ratcliffe, Jebrael Nokandeh, Amin Nazifi, Richard Thomas, Rowena Gale & Birgitta Hoffmann, Iran, Vol. 45, No. 1, 95-136, DOI: 10.1080/05786967.2007.11864721, 2007.
  8. Detection and Documentation of the Red Snake by means of Remote Sensing Techniques, Abbass Malian, Jamaledin Mahdinejad & Somayeh Aslani, Journal of Interdisciplinary Research, Vol. 7, No. 2, pp. 125-138, 2017.