Largest ancient fortress of South-West Asia and the western world? Recent fieldwork at Sasanian Qaleh Iraj at Pishva, Iran

Protected by a massive wall, but devoid of permanent buildings in its vast c. 175 ha interior, the rectangular compound of Qaleh Iraj near Tehran must be a military base – and as such, it is arguably the largest fortress in the ancient world to the west of modern Afghanistan. Investigations carried out previously have been based on surface finds and architecture and there had been no agreement on the date and purpose of this monument. Excavation, survey, in-depth studies of its architecture, satellite images and historical sources and the application of scientific dating have now enabled us to precision-date the earliest activity in the south-eastern gateway and the likely construction date of the fortress and to place it in its proper historical context. Sasanian Qaleh Iraj may have played a pivotal role in the northern defensive network of one the Ancient World’s most powerful empires and the fortress sheds significant new light on its military capabilities.