The Arg-e Bam is the largest adobe building in the world, located in Bam, a city in Kerman Province of southeastern Iran. It is listed by UNESCO as part of the World Heritage Site "Bam and its Cultural Landscape". The origin of this enormous citadel on the Silk Road can be traced back to the Achaemenid Empire (sixth to fourth centuries BC) and even beyond. The heyday of the citadel was from the seventh to eleventh centuries, being at the crossroads of important trade routes and known for the production of silk and cotton garments.
The entire building was a large fortress containing the citadel, but because of the impressive look of the citadel, which forms the highest point, the entire fortress is named the Bam Citadel. Wikipedia