Hasanlu Tepe is critical to our understanding of the development of architecture and urban form in northwestern Iran. Hasanlu's archaeological significance centers on its long occupational sequence, achieved by deep soundings on the High and Low Mound, the amazing state of preservation in its early Iron Age levels and the large horizontal exposures excavated on the High Mound. The High Mound was occupied fairly consistently from the Neolithic to the later Iron Age (Period II) and was probably always the main focus of settlement. Knowledge of the Neolithic, Chalcolithic and Bronze Age urban layout and architecture is limited due to the substantial overlying Iron Age strata. The area of the Low Mound was probably first utilized in Period VII, or the earlier 3rd millennium BC. This area was probably occupied until the end of Period VI, equivalent to the Middle Bronze Age in Mesopotamia (2000-1600 BC). In the limited areas sampled on the Low Mound, it appears this area was not extensively used for settlement in the early Iron Age, although further research must be conducted to delimit the area of the Iron Age settlement.
In the Bronze Age, Hasanlu was probably quite similar in terms of its urban form and developmental sequence to the fortified towns and cities of northern Mesopotamia (kranzhügel), consisting of an inner fortified city and a fortified outer town, although no evidence for outer fortifications was ever discovered due to modern agricultural activities and the presence of the modern villages of Hasanlu and Aminlu on the edges of the Low Mound.
The High Mound
During the earlier Iron Age (1200-800 BC; Periods V and IV), the High Mound served as a fortified citadel containing many monumental structures such as palaces, temples and arsenals. The hallmark of this period is the columned-hall structure, typical of the monumental architecture of western Iran in the early Iron Age and first attested at Hasanlu V and IV. Following the destruction of the citadel at around 800 BC, probably by the Urartians of the Lake Van region, the High Mound was temporarily abandoned before it was chosen as the site for an Urartian fortress (Period IIIb). This structure is one of the better-preserved Urartian fortresses, though it is atypically located on a large, commanding hill or rocky outcropping. This fortress was burned, rebuilt, and burned a second time. The site was then abandoned long enough for a ruin mound to form. For a time, the High Mound was used as a cemetery. On top of these ruins and the cemetery, new monumental structures, one probably in the columned-hall tradition, were constructed in the Achaemenid and Seleucid Periods (Period IIIa/II) on the southern High Mound, and modest fortifications were built to protect the area of the High Mound. The High Mound was abandoned in the 3rd century BC. Following a hiatus in settlement of 1500 years, the High Mound was reoccupied as a hillfort in the Medieval Period (Period I).
In the Iron Age, architecture at Hasanlu usually consisted of a fortified citadel containing monumental structures and was similar to later sites of the Iron Age III in western Iran such as Godin Tepe and Nush-i Jan. Hasanlu probably served as a central place for a largely transhumant tribal population living in the surrounding valley and uplands.
The Low Mound
The Hasanlu Project completed few large horizontal clearances on the Low Mound, and so the architecture of this area, likely residential in nature, is largely unknown. The Low Mound was first occupied in Period VII or the Early Bronze Age (3000-2000 BC). It does not appear to have been heavily occupied in the Iron Age, although many areas could not be sampled by the project due to modern cemeteries located there. In the Bronze and Iron Age, the northeastern Low Mound was used as a cemetery.