Falak-ol-Aflak

During the Elam period (3200 - 539 BC), Khaydalu was a ancient city.^[5] In 640 BC, Ashurbanipal, the king of the Neo-Assyrian Empire, conquered Elam and destroyed Khaydalu.^[6] Afterwards, the city became a part of Assyria.^[7][8] During the Achaemenid Empire, Lorestan and Khaydalu, along with Ilam and Khuzestan, were the states of the empire. During the Parthian Empire, it was also one of the states of the empire, and finally, during the Sasanian Empire, a new city named Shapur Khast was built by the order of Shapur I upon the ruins of Khaydalu, with this castle being the most important structure of that city.^[9][10]

The castle was used for government and military purposes during the Sassanid Empire.^[11] After the Muslim conquest of Iran and at the end of the Uthman rule (656 AD), the people of Shapur Khast revolted and stood up against the Arabs, which shows the great importance of the city at that time.^[12] Due to its excellent strategic location, the castle became the seat of Hasanwayhid (959 - 1015 AD) and Buyid (934 - 1062 AD) governments.^{[13][14][15][16]}

Shapur Khast was completely destroyed and deserted after the Mongol invasion of Iran, with the Falak-ol-Aflak castle being the only building that was not destroyed because it was strategically beneficial for the mongols, so they settled in.^[17][18] The people of Shapur Khast moved to the western part of the castle, which was superior in terms of having plenty of water and a more convenient location as well as security. The name Shapur Khast can be seen in the old books until the beginning of the 7th century, but after the 8th century, the name of the city was changed to Khorramabad. With the Iranian Intermezzo taking place, the castle became the government seat of Khorshidi dynasty (1184 - 1597) and the governors of Lorestan during the Safavid Empire (1501 - 1736).^{[19][20][21][22]} During the Qajar period (1789 - 1925), the castle was also important for various reasons. Qajar statesmen used to come and go to the castle a lot, with some of them left notes about the it.^{[23][24][25][26][27]}

During the Pahlavi period (1925–1979), the castle was used as a prison and became a storage place for ammunition, including mines and explosives,^{[28][29][30][31][32]} After the Iranian Revolution, the museum of archeology was opened in 1999, and in the same year, the northern part of the courtyard was converted into a tea house.^[33] In 2000, a restoration laboratory was opened in the southern part of the first courtyard.^[34]

The castle is considered as one of the architectural masterpieces, because it is built with a system of moisture-absorbing channels.^[35][36] The castle includes a moisture absorbing system.^[37] The castle is built with materials such as stone and wood, which are vulnerable to moisture.^[38] For this reason, it was built at the highest point of Khorramabad city, so that the wind penetrates inside the building and dries its foundations.^[39][40]

• Sassanid architecture
• Iranian architecture

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• Lorestan Province Cultural Heritage Organization