It's a sad fact of archaeological life that we can often only find things when they're about to be lost forever, but such is the unhappy marriage between rescue archaeology and infrastructure development. Construction of the Ilisu dam, on the river Tigris in southeast Turkey, is now complete and the flooding of 300km2 of land behind it may begin as early as this spring. The dam will provide water security and electricity to the local region, as well as further restrict the diminishing flow of water downstream to Iraq, displace at least 70,000 people and flood up to 500 archaeological sites.
Leaving its tangled politics aside, the Ilisu dam represents a substantial loss of cultural heritage in this archaeologically rich area, most notably the well-publicised destruction of the beautiful and ancient town of Hasankeyf. However, it has also provided a great opportunity to learn about the past of this region.
When the dam was green-lit in the early 1990s, the Turkish government invited teams of local and international archaeologists to work in the Tigris basin upstream of Ilisu to recover as much as possible before the dam was completed. The result was a series of intensive survey projects, followed by more than twenty excavations, which uncovered sites ranging from deep prehistory to the Ottoman period. The area to be flooded is now the best-studied archaeological landscape in eastern Turkey.
One of the biggest Ilisu dam salvage excavations was at the site of Ziyaret Tepe; an imposing occupation mound rising 22 metres above the plain, within which lies the ancient Assyrian city of Tušhan.
Tušhan was a provincial centre which guarded the northern border of the mighty Assyrian empire for almost 300 years (882-611 BC). It never approached the grandeur of an Assyrian capital such as Nineveh, but it was part of the Assyrian network of imperial control which imposed the "Yoke of Assur" over conquered regions. Tušhan was home not just to Assyrian settlers, but to deportees from all over the empire, uprooted from their homelands as a further means of subjugation.
Work at Ziyaret Tepe began in 1997 and ran for eighteen years; long enough for students to graduate into academic careers, and for the director's hair to turn grey. In 2003 I arrived at the site as a fresh archaeology graduate without the faintest idea what I was doing, not thinking for a moment I'd still be digging there ten years later. The results of all those long sweltering summers in the field are now finally ready to be presented, with the publication this year of the project's first book. It provides the most complete picture of an Assyrian imperial town yet known.
Ashurnasirpal II, as depicted in his royal palace at Nimrud. This panel is on permanent display at the British Museum. The king is shown in profile holding a shallow bowl in front of his face.
Ashurnasirpal II, as depicted in his royal palace at Nimrud. This panel is on permanent display at the British Museum. Photograph: Graham Turner for the Guardian
The governor's palace at Tušhan, which sits on the eastern side of the high mound, was built under king Ashurnasirpal II, who boasted about its construction in an inscription found not far from the site. Unlike Ashurnasirpal's magnificent Palace at Nimrud, the throne room of which can be seen in the British Museum, Tušhan's provincial palace had no stone reliefs. Instead its white plastered walls were decorated with finely painted geometric patterns in blue, red, orange and black. The reception suite was equipped with a trackway for a moveable heating brazier and neatly tiled bathroom facilities, giving it a touch of luxury.
Some of the governors themselves may have been located. Under the paving of the palace courtyard five intact cremation burials were excavated. Whether or not these were the governors of Tušhan, they were certainly important people, cremated on beds with ivory fittings, and provided with bronze bowls, lamps and ornaments. Intriguingly, cremation was not an Assyrian practice and these burials suggest that Tušhan's ruling elite had either adopted local customs, or were not themselves Assyrians.
To the south of the high mound, Tušhan had a substantial lower town and this is where the real work of the city took place. Over many seasons the excavation team uncovered a series of large buildings, all set around courtyards paved with beautiful black and white chequerboard mosaics made of thousands of small, smooth river pebbles. Most were high-status houses but one had more complex functions. The entrance chamber to this building yielded hundreds of tiny clay tokens; small clay objects in a range of shapes standing for different numbers and commodities. These little pyramids, spheres, cylinders, cones, squares and cubes are thought to have been used as accounting tools, for keeping running-records as goods and people passed in and out.
The administrative function of the building was confirmed when an archive of 28 cuneiform tablets was found in two rooms off the main courtyard. These include lists of personnel, a record of resettlements and the loan of a slave, but most concern the movement of barley. These transactions are visible throughout the building in the form of standardised weights and huge pithoi for grain storage. This building was a commercial and administrative hub of Assyrian Tušhan.
The frontier character of the city, on the border with hostile Shubria, is clear from the massive fortifications which surrounded both the high mound and the lower town. The mudbrick city wall was two kilometres long and almost three metres thick with a substantial ditch in front of it. The excavated southern gateway was heavily fortified, with guard chambers on each side and troop barracks close by.
Despite these precautions, Tušhan fell with the rest of the Assyrian empire, conquered by a coalition of Medes and Babylonians. The imperial capital at Nineveh fell after a dramatic siege in 612 BC, after which the remaining Assyrian forces retreated steadily north-westward towards the empire's last stand at the city of Harran. In the path of the Medes and Babylonians as they marched up the Tigris river lay Tušhan.
It was at this point in 611 BC that an official in the city called Mannu-ki-libbali wrote a letter which was never sent and constitutes one of the most extraordinary finds from Ziyaret Tepe. It details the collapse of the empire's logistical framework and describes the hopeless position of Tušhan in the face of the advancing enemy.
Now Tušhan faces another final enemy, as over the next couple of years the water from the Ilisu dam advances along the same route as that used by the Medes and Babylonians 2,600 years ago. It remains to be seen to what extent the site will eventually be flooded, but even though its physical remains may be lost, along with the other Ilisu sites, there is some consolation in the fact that a rich record of the town of Tušhan, its history, people and way of life, is now preserved in the archives and publications of the Ziyaret Tepe project.