Pāpak Fort () or Babak Castle (), ″Ghal’eh-e Baz″ is a large citadel on the top of a mountain in the Arasbaran forests, 50 km from Ahar, one parasang from Ardabil, 6 km southwest of Kalibar City in northwestern Iran. According to Ibn al- Nadim, it was the stronghold of Javidhan and Babak Khorramdin, the leaders of the Khurramites in Iranian Azerbaijan who fought the Islamic caliphate of Abbassids. The fort was conquered and ruined by Afshin′s army in 837. Access The castle is built on 2300–2600 meter heights and is surrounded by 400 to 600 meter gorges. Access to the castle can be found using a long series of broken steps that lead to the top of a hill. After that, the easiest route is a long dirt track. At the end of the dirt track, the route turns left. The first sign of the ruins appears on the left, leaving two peaks to cross. The first peak has views of the castle. After ascending a second peak with additional ruins, the trail passes sheer cliffs on the right with no railings. The surrounding Arasbaran oak forest, jagged cliffs and mountains in the distance can be seen from the castle. The last stretch to the main castle is a narrow passageway and a 200-meter corridor-shaped temple. The castle is nearly impossible to capture, due to it being high in the mountains and protected by ice and snow. History The castle is believed to belong to the Parthian dynasty, with modifications under the Sasanid dynasty. Khurramites in the fort The movement of Khurramites in Azerbaijan was associated with Javidhan who was a landlord leader of one of the two Khurramite movements in Azerbaijan (from 807-808 to 816-817), with his headquarters being in Badd, located close to the Aras river. The leader of the other Khurramite movement was Abu Imran, who often clashed with Javidhans forces. During one of the clashes, in probably 816, Abu Imran was defeated and killed, whilst Javidhan was mortally wounded, dying three days later. Javidhan was succeeded by his apprentice Babak Khorramdin, who also married Javidhan's widow. Tabari records that Babak started his revolt in 816–817. At first, Al-Ma'mun paid little attention to Babak′s uprising because of the difficulty of intervening from distant Khorasan, the appointment of his successor, and the actions of al-Fadl ibn Sahl. Such conditions paved the way for Babak and his supporters.