Archaeology
The ancient road between Al-Ula and Al-Wajh
Al-Ula
Al-Ula is one of the oldest cities in the Arabian Peninsula and home to Hegra, a UNESCO World Heritage site. Mada’in Salih, the ancient city of Hegra, is a rich land in historical, geological, and geographical significance.
The Nabataean kingdom occupied Mada’in Salih in the fourth century AD. Since then, Mada’in Salih had become a major political centre and a significant commercial emporium during the role of the Nabataean. Therefore, there is a potential for ancient trade and communication routes from Al-Wajh on the Red Sea littoral in Tabuk province to the ancient settlements of AlUla (Madaʾin Salih). Also, from Mada’in Salih to the northwest to Petra, the capital of the Nabataean kingdom, passing through the oasis of Shawaq and Disa town. This ancient trade is part of ancient commercial centres and the trade routes in the red sea area. Therefore, the traders coming from or going to southern and eastern Arabia had to pass Mada’in Salih.
Focusing on the movement, an important field of study in the modern archaeological approach, in one part of ancient trade during the Nabataean role. The potential ancient trade focused on is between Mada’in Salih in Al-Ula and Leuke Kome port (Al Quisar) in Al-Wajh.
The Nabataean kingdom
There is a potential for ancient trade and communication routes from Al-Wajh on the Red Sea littoral in Tabuk province to the ancient settlements of AlUla (Madaʾin Salih). Also, from Mada’in Salih to the northwest to Petra, the capital of the Nabataean kingdom, passing through the oasis of Shawaq and Disa town. This ancient trade is part of ancient commercial centres and the trade routes in the red sea area. Therefore, the traders coming from or going to southern and eastern Arabia had to pass Mada’in Salih.
Ancient trade and communication routes
Study focus
Study Objectives
Discussing and analysing the studies that have been using GIS to determine the Least Cost Path (LCP) in the ancient trade between Mada’in Salih and Leuke Kome port—also discussing the pros and cons of using GIS in studying the movement.
Study Area
Least-Cost Path Calculations
Different Least-cost paths were calculated:
The least-cost paths (Route 1 and 3) were calculated by applying only the slope value. Mada’in Salih was chosen as an origin point and AlQuisar as a destination point in Route 1. Whereas in Route 3 AlQuisar was chosen as an origin point and Mada’in Salih as a destination point.
The second least-cost paths (Route 2 and 4) were calculated by applying the friction values algorithm: [((slope value)2 (0.031))-((slope value) (0.025))]+1. In Route 2, Mada’in Salih was chosen as an origin point and AlQuisar as a destination point. Whereas Route 4 vis versa.
Route 5 and Route 6 are the least-cost paths from Mada’in Salih to Al-Wajh. Route 5 was calculated by using only the slope. Whereas in Route 6, the LCP was calculated using the friction values algorithm.
LCPs were calculated after changing the map projection of the DEM from (GCS_WGS_1984) into (WGS_1984_UTM_Zone_37N) as well as the unit length of the DEM to notice any changes in the path.
RESULTS
Case study: Least Coast Calculations Using GIS
"The al-'Ula –al-Wajh Survey Project" used two methods to reconstruct the least-cost paths (LCPs), which are more complex than calculating least-cost networks, between Mada’in Salih and AlWajh.
The first method used only the slope layer in calculating the LCPs.
The second method used the friction values algorithm.
Even though they very clearly present the resolution of the digital elevation model (DEM), the source of the DEM, and which model of GIS software they used to calculate the least-cost paths, there is much information related to the data sets needed to be mention in their study. First of all, they did not mention the slope unit they used in calculating the LCPs. The slope has a significant effect on the results, leading to different cost function results.
They did not mention the city they chose as an origin point as well as the destination point. Even though the results came as the same when I applied their methods from Mada’in Salih to AlWajh and from AlWajh to Mada’in Salih (vice versa), they should mention that to validate their model and use it probably in some other studies.
LCPs of their survey project were calculated several times. Each time I used their first method (only the slope), the result was their route for their second method (friction values algorithm). Also, when I used their second method, the result came as their route for the first method. I came up with several assumptions for that: the first assumption is that the lack of information about their formula leads me to misunderstand the formula. The second assumption is that they made a mistake in writing the number for each route.
Discussion
Discussion of Least Coast Calculations using GIS
Here are some technical aspects of calculating the LCPs using GIS:
Calculating least-coast paths using ArcMap allows the path to move only in eight directions only. On other words, the movement through the route is limited to only eight moves in each cell of the slope. That is one of the drawbacks of using ArcMap.
The high resolution of the DEM is very important. On the other hand, computation times increase considerably when using high DEM resolutions, especially with large study areas.
It is not important to look through the map projection of the DEM or your layers as long as they are in the same map projection. I have experienced that by calculating the least-cost paths in two different map projection.
Changing the orientation of the coordinate system by a few degrees could result in completely different paths.
The length unit that shown in the layer properties whether is empty or meter, it does not affect the result of the LCPs. That has been proven by observing the changes before and after changing the length unit from an empty space into one meter.
Conclusion
Mada’in Salih is a rich historical, geological, and geographical significance land. It played a significant role in the economy of the Nabataean Kingdom. Therefore, more studies should focus on the movement in the area.
GIS is a magnificent tool. It has helped in the archaeological field in almost every aspect of it. Calculating the least-cost paths is a critical use of GIS in archaeology. Many researchers have developed the tool in GIS by manipulating the data, especially with the digital elevation model (DEM) and the slope. Also, they stimulated the ancient route and communication ways by creating many barriers and considering many factors. Although the archaeologists have done plenty of development in calculating the movement through GIS, it still does not entirely rely on it. The researchers should use the calculation of LCPs through GIS as a first result in identifying the most suitable routes. Then, validate the GIS calculation of the LCPs by collecting data from GPS trails, for example.
Calculating the least-cost path through GIS for the ancient route between Mada’in Salih and AlWajh has not successfully reached a reasonable output. Therefore, I used the GIS to confirm "The al-'Ula –al-Wajh Survey Project" as well as to experience several technical aspects.
