Falak-ol-Aflak Castle (in Persian: دژ شاپورخواست Dež-e Shāpūr-Khwāst, in ancient times known as Dežbār as well as Shāpūr-Khwāst) 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 .