| Shapur Khast | |
| Native Name: | Persian: دژ شاپورخواست |
| Location: | Khoramabad, Luristan, |
| Coordinates: | 33.4837°N 48.3534°W |
| Map Type: | Iran |
| Est Completion: | Sasanian era (224–651) |
| Building Type: | fortress |
Falak-ol-Aflak (Persian: فلک الافلاک|lit=the sky of the skies) or Shapur Khast Castle (Persian: دژ شاپورخواست) 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 Sassanid era (224–651).[1]
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.
Under the Pahlavi dynasty, after being used as a prison until 1968, it was transformed into a museum complex.
The foundations of the actual castle measure approximately 300x. The height of the entire structure, including the hill, reaches 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 Khoram-abad, so that the wind could penetrate the building and dry its foundations.
The castle is managed by the Iran Cultural Heritage Organisation and a protected site.