Evidence for ancient irrigation agriculture in the hinterland of Gadara/Umm Qeis, northern Jordan
Bernhard Lucke a, Sufyan al-Karaimeh b
a FAU Erlangen-Nürnberg
b Leiden University
The ancient city of Gadara (today Umm Qeis) in north-western Jordan had been built on a mountain saddle between a basalt plateau with most fertile soils, and rocky limestone hills with widespread caliche crusts. No spring was located at the site, which made it necessary to collect rainwater, to carry water from springs located downhill, and to channel water by aqueducts to the site. Such aqueducts and water tunnels supplied the city first on a local scale, tapping water from a nearby spring, while it was connected to a regional water supply system during the Roman period, the “Qanat Firaun”, which is the longest known aqueduct of antiquity. It distributed enormous quantities of water to the cities of the ‘Decapolis region’, connecting Gadara with springs of the southern Hauran in present-day Syria.
Little is known about the wastewater management, agriculture, and landscape change in the vicinity of the site. The caliche-covered limestone hills, today hosting one of the last intact forests of the deciduous Quercus ithaburensis of Jordan, has often been considered the degraded remains of large-scale soil erosion due to overgrazing and mismanagement, in particular during the Islamic period. However, numerous rock-cut channels were found in the crust and could be traced over long distances. The channels divided into branches, junctions and outlets to supply water to the slopes, probably for irrigation purposes. Although bare rocks prevail in the largest part of the today forested limestone hills, few remains of ancient terrace systems were preserved in some areas. These were discovered following the course of the channel remains. Two test trenches revealed the following features:
- Caliche crust and carbonised roots at the bottom suggest that the terraces were constructed on forest covered rocks similar to the current landscape.
- Fist-sized stones were the main building material. Only near a developing gully larger stones were used, probably to reduce or stop its erosive power.
- The pottery assemblage throughout the profile suggest continuous use and sedimentation from the Hellenistic till Byzantine-Umayyad period.
- Gully erosion apparently started to become a problem during the Byzantine time, and repeated erosion events seem to have cut off the terraces from its irrigation supply channels shortly after attempts to repair gully cuts.
Since the area is located in a small clearing of the forest and still provides rich pasture, it seems likely that it was grazed longer and more intensely than other slopes that lost their terraces and were reforested more quickly.
These discoveries suggest that intensive irrigated agriculture had been carried out in the hinterland of Gadara during classical antiquity, using wastewater from the aqueducts, and taking advantage of the caliche crusts for water harvesting and channel construction. However, most of these terraces were seemingly lost to erosion of the steep rocky slopes, possibly due to the occurrence of heavy rains and earthquakes during the Byzantine-Umayyad time.