What is an iwan and how was it used in Parthian palaces?

An iwan is a large, three-sided hall or audience chamber characterized by an open archway that replaces the fourth wall.1

In Parthian architecture, the iwan served as a distinctive feature of palaces and private houses. These structures were often designed with multiple iwans, and their adjoining facades were frequently decorated with engaged columns arranged in single or tiered rows, reflecting an influence from classical architectural orders. Notable examples of this design can be found in the Parthian palace at Ashur and the fortress city of Hatra. This architectural element became a significant influence on later Islamic architecture.1