Using GIS to Increase our Understanding of Ancient Jordanby Gary L. Christopherson, Dr. Philip Guertin and Karen A. Borstad, University of Arizona, USA. |
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GIS technology is a powerful tool for helping people understand how they are shaped by their environment, and how they affect their environment. These capabilities make it an ideal tool for archaeologists analyzing ancient civilizations.
In many ways Jordan is an archaeologists dream, with fantastic monuments such as Petra, well preserved Roman cities like Jerash, hundreds of typical Near Eastern talls (settlement mounds), innumerable small archaeological sites, and pottery sherds that are, quite literally, everywhere one looks. As attention in the region turns from conflict to cooperation, the discovery and management of these cultural resources is becoming increasingly important.
The Madaba Plains Project (MPP) has been involved in the archaeology of Jordan since 1968, discovering hundreds of sites during surveys of the Madaba region and conducting excavations at the sites of Tall Hisban, Tell El-Umayri, and Tall Jalul. Since 1991, the MPP, in cooperation with the Advanced Resource Technology Group and the Near East Studies Department, at the University of Arizona, has incorporated ESRI's ARC/INFO GIS as an integral component of the project.
Settlement Patterns and GIS
In the early 1970's, a distinctive, cyclical pattern was noted in the ceramics collected by excavation and survey teams. The pattern indicated that settlement periodically intensified, then abated in the region. It was suspected that these cycles were in some way tied to the environment, but making a concrete connection had proven difficult. In 1991, this connection was made when the MPP began using ARC/INFO to build probability models for archaeological sites from the Tell el-Umayri regional survey. Conducted within a five-kilometer radius of the main excavation site, the regional survey has documented 131 archaeological sites ranging in age from the lower Paleolithic to late Islamic, and in size from urban centers to small, seasonal encampments.
Probability models were constructed for Iron Age I (ca. 1200-900 BCE) and Iron Age II (ca. 900-500 BCE) sites (a transition from low to high settlement intensity). Thirteen environmental factors were analyzed along with archaeological data to determine the respective typical local environment, or environmental signature for each age.
The differences in the strengths of the environmental signatures indicate that there were definite connections between the environment and locational strategies in the Umayri region. Iron Age I sites were located in narrowly focused environmental zones. Their strong environmental signature is indicative of a population settling on prime agricultural land. On the other hand, Iron Age II sites were scattered throughout the environment, resulting in a weak signature. This suggests that population pressures were forcing people to settle in less favorable environmental zones and to adapt subsistence strategies as a result.
Extending this logic, it is possible that as available lands became more environmentally marginal, survival pressures continued to build until a crisis point was reached when environmental and social constraints met head on with the pressures of population growth. The result would be a cyclical pattern of settlement intensification and then sudden, periodic collapse.
Iron Age Agricultural Practices
Throughout history, soil erosion and water conservation have been important considerations in agriculture. This is especially true in the arid and semi-arid Near East, where intensive agricultural practices, including the construction of agricultural terraces, have been used for millennia.
Ancient terraces litter the slopes around the Madaba Plain, but discovering their age by conventional archaeological means has proven nearly impossible. This lead to an ongoing debate over whether terrace-based agriculture was introduced during Iron Age I or Iron Age II. Because it requires a great deal of effort to build and maintain terrace systems, it has been suggested that they were not introduced during Iron Age I, a period of relatively low population, but more likely during Iron Age II in response to the pressures of an expanding population.
To address this question, a series of grids were
built in ARC/INFO, using the Universal Soil Loss Equation
(USLE), which described potential erosion under a variety of
conditions in the Umayri region. Models were built for a
landscape with natural vegetation intact, for a deforested
landscape, and for a deforested landscape being cultivated
for agriculture. Erosion potential in these models was
classified as low (<10 metric tones/hectare/year), medium
(10-50 metric tons/hectare/year), and high (>50 metric
tons/hectare/year). The results show that with natural
vegetation intact, there is little potential for erosion in
the region. If vegetation were removed, erosion potential
increases dramatically. Erosion potential increases even
more dramatically if the cleared land is cultivated.
Assuming that areas with erosion rates above 50 metric
tons/hectare/year could not be successfully farmed without
conservation structures, it was clear from these models that
terraces would be necessary for agriculture to be successful
in about 24% of the Umayri region.
Archaeological sites were then buffered by 100 meters and overlaid on the erosion models, with the expectation that farmers would prefer optimal agricultural zones, i.e. those with the best soil and the lowest erosion potential. Not surprisingly, 84% of the land surrounding Iron Age I sites had the best agricultural soil. Very surprisingly, 42% of the land surrounding Iron Age I sites lay in areas of the highest erosion. Clearly, erosion potential was less important than soil type when choosing where to settle, indicating a high probability that terraces were used by Iron Age I farmers in the Umayri region
This conclusion was supported by the results for Iron Age II sites. It is known that terrace agriculture played a significant role in the Iron Age II economy. If subsistence strategies were significantly altered from Iron Age I to Iron Age II, this would be reflected by differences in the location of settlements. Instead, more similarity than dissimilarity was found. Again the most important factor was soil type, with 72% of the land surrounding Iron Age II sites having the best agricultural soil, and 43% located in zones of the highest erosion potential. Based on these results, it seems most likely that terrace agriculture was introduced during Iron Age I in the Umayri region, and continued to be important during Iron Age II.
GIS and Archaeology
The potential of GIS to help archaeologists understand
how ancient people were influenced by, and in turn
influenced their surrounding environment is tremendous. GIS
allows a researcher to see and examine inter-site patterns
and make inquiries into how people lived. This kind of power
means that the use of GIS technology, such as ARC/INFO, in
Near Eastern archaeology will continue to grow as
archaeologists use it to examine the relationship between
ancient people and their environment.