Falak ol-Aflak () or Shapur Khast Castle () is a castle situated on the top of a large hill with the same name within the city of Khorramabad, the regional capital of Lorestan province, Iran. This gigantic structure was built during the Sasanian era (224âÂÂ651).
The Khorramabad River runs past the eastern and south-western side of the Falak-ol-Aflak hill providing the fortress some natural protection on those sides. Today, the western and northern sides of the hill are bordered by the residential districts of Khorramabad.
During the Pahlavi era, after being used as a prison until 1968, it was transformed into a museum complex.
The foundations of the actual castle measure approximately . The height of the entire structure, including the hill, reaches up to 40 meters above the surrounding area.
Archaeological studies have identified the existence of a two layered rampart with twelve towers around the present day construction. From the twelve original towers, only two remain and these are situated northwest and southwest of the existing fortress.
Falak ol-Aflak castle is made with different materials like stone and wood that are vulnerable to humidity. That is why the castle was built on the highest point of the city of Khorramabad, so that the wind could penetrate the building and dry its foundations.
The castle is managed by the Iran Cultural Heritage Organisation and is a protected site. During the 2026 Iran war, the castle received structural damage from US strikes.