A vaulted open hall with a rectangular or arched facade. The iwan is a Persian invention that worked well as an entrance of a mosque, an entrance to the prayer hall or the prayer hall itself. The combination of four iwans arranged axially around a courtyard became one of the most important plans of religious buildings in the Muslim world. The qibla iwan (sanctuary iwan) was always the largest and the deepest. The opposite one was next in size and the other two were the smallest. (see Islamic Art Glossary).