From 1979 to the present, the Yale University Tell Leilan Project has been excavating at Tell Leilan,
Our work at Tell Leilan has focused on the dynamic relationship between humans and their natural and social environment. Specifically, we have analyzed the rise of the state at ca. 2600 BC, the Akkadian imperialization of Northern Mesopotamia at ca. 2300 BC, the collapse of settlement following an abrupt aridification event at ca. 2200 BC, and the subsequent resettlement of Northern Mesopotamia, which was coincident with the creation of Tell Leilan (Šubat-Enlil) as one of the capitals of Šamšī-Adad's North Mesopotamian Kingdom at ca. 1800 BC. In order to investigate these periods of social, political and environmental change, we have excavated large horizontal exposures of religious, political and domestic architecture at the Acropolis, Lower Town and along the City Wall. We have analyzed the regional settlement landscape during these periods for the spatial distribution of resettlement and for social and natural alterations in settlement growth and decline. The data retrieved from these excavations and regional surveys have been analyzed by zooarchaeologists, archaeobotanists, soil micromorphologists, geomorphologists, Assyriologists and other specialists to aid our reconstruction of third and second millennium BC economy and society in North Mesopotamia ( Figure 2 ).
There have been two major excavations on the Leilan Acropolis. In the Acropolis Northwest, excavations from 1979 until the present have focused on a large administrative area. In the far west, Operation 1, a step-trench down the western side of the mound, allowed us to document the 4,000 years of settlement at Tell Leilan and create a ceramic chronology for the site. Adjacent to Operation 1, the Acropolis NW sounding is a 2400m2 exposure of a third millennium palace complex, originally constructed at 2600 BC, coincident with Leilan's urbanization. This complex contains a series of storage rooms, a cultic platform, industrial installations, massive fortification walls, a 25 m tall glacis to the north, and a wide moat in the southeast. This palace complex was surrounded by open space, which probably emphasized its actual and symbolic presence. Excavations have revealed 12 phases of this space (strata 17-6), spanning nearly 500 years, from its initial construction to the extensive Akkadian renovation of this area. In the Acropolis Northeast, excavations from 1979-1985 revealed a large second millennium temple, probably constructed by Šamšī-Adad, when he made Šubat-Enlil his main residence after conquering Northern Mesopotamia. Elaborate spiral and palm-tree columns ornamented the façade of this building, as they did contemporary temples at Tell ar-Rimah, Larsa and Ur in Iraq. The shared iconography of these temples is mirrored by the language used in the cuneiform tablets found here; like many documents in second millennium Northern Mesopotamia, they were written in the "Southern dialect" of Old Babylonian, rather than in the local language. The excavation of the Acropolis temple provides evidence for the adaptation of foreign ideology which encouraged the resettlement and political unification of Northern Mesopotamia in the early second millennium BC.
In the Leilan Lower Town and along the City Wall, excavations have focused on second and third millennium remains and include the excavation of two second millennium palaces, second and third millennium levels at the "City Gate", a second millennium neighborhood along the city wall and a third millennium workers' neighborhood. The first palace, the Eastern Lower Town Palace, was probably built by Šamšī-Adad and was the main palace at Tell Leilan during the second millennium BC, until Samsu-iluna of Babylon killed the last king of Šehna and destroyed the city in 1728 BC. Three separate archives of tablets (totaling more than 600 tablets) were found during the excavations of this palace: a wine archive, a mixed administrative archive, and the diplomatic archive of the last three king's of Leilan, which included letters and rare treaties that shed light on a period of Mesopotamian history which had been previously documented. The second palace, the Northern Lower Town Palace, belonged to Qarni-Lim, a powerful king of the neighboring city of Andarig, who established de facto control over Tell Leilan not long after the death of Šamšī-Adad. An archive of 651 tablets relating to the manufacture and delivery of beer was found in the palace, which probably contained a brewery in the unexcavated area. Excavations at the City Gate established that this area was first constructed at 2600 BC, when the Lower Town was first built and was rebuilt and maintained until the final abandonment of the city ca. 1700 BC. It also exposed an administrative area where custom's officials controlled the entrance into the city during the third millennium. Near the City Wall, excavations uncovered rare private houses from the second millennium BC, which contrast with the monumental architecture that we have recovered. Finally, the third millennium worker's neighborhood in the Lower Town South exposure contained a number of houses along a wide street, which probably connected this quarter to the Acropolis. Excavation once again revealed several phases of occupation over 400 years, from roughly 2600-2200 BC.
In all excavations at Tell Leilan, we have encountered a 1-2 m deposit of wind-blown sand, with no architecture and few pottery sherds between the third millennium and second millennium levels. This lens dates to the abandonment of the city from 2200-1900 BC, an abandonment which occurred during a three-hundred year cold and dry abrupt climate change which is present in paleoclimate proxy records across the eastern and western hemispheres ( Figure 3 ).
A full understanding of social processes in Northern Mesopotamia requires high-resolution regional settlement data. To this end, the Tell Leilan Regional Survey (1981, 1984, 1987, 1995, 1997), a continuing research effort, has documented the regional occupational history over the last 10,000 years using well-dated, short period diagnostic indices, varieties of satellite imagery, and GPS mapping. The survey transect is 30 Kilometers and extends from the Iraq border to the south and to the Turkish border to the north, ca. ___Km2.