This one-of-a-kind monument belongs to Sassanid period and it has been registered in the list of Iran's National Heritage under the registration number of 883. There is no accurate information about when and by whom it was built. We just know that the monument is a remaining from "Shāpūr-Khwāst" ancient city. The initial building of the castle is attributed to the reign of Sassanid Shapur I in century 3 AD. The beauty and wonderful architecture of Falak-ol-Aflak Castle has convinced many experts to consider this ancient historical castle of Lorestan Province as one of the engineering and architectural masterpieces.
Since the construction of Sassanid period ports up to recent periods (especially in Safavid and Qajar periods), some things have been added to the castle, and this fortress is the same well-known Shāpūr-Khwāst Fortress which is mentioned in the history.
Due to its strategic position, this castle was selected as the seat of government of Hasanawayhids and as the treasurer in Buyid dynasty in the 4th century AH. Since the 6th century AH when the new city of Khorramabad was built, the castle became also known as Khorramabad. The name of Falak-ol-Aflak might have been given to it in Qajar dynasy.
There are two museums of anthropology and archeology in Falak-ol-Aflak Castle Complex that are considered as the attractions of Khorramabad.