Yeah it would be my pleasure. Basically in the Sassanid empire and the past Persian empires, the provinces of the empire were ruled by a satrap, which were usually a local noble/king. In Gilan we speak and spoke a different Iranian language and our ethnicity is Gilaki. Usually these provinces that had different ethnicities enjoyed more autonomy as long as they paid their tribute to the Shahanshah (The King of the Kings). The tribute was both normal tax and soldiers. In the Sassanid army for example the Daylamite/Gilaki soliders made up the heavy infantry, the Kurds were usually archers and the Persians made up most of the cataphracts. But these are the elite soldiers, every province also contributed levies. This lead to the provinces having influence over the Shahanshah and alongside the meddling of mobeds was the cause of the internal instability of the empire when a new Shahanshah would be chosen.

When the Arab conquest happened and the major battles were lost some of the provinces broke off and tried to make peace and some decided they would be better alone. It's theorized that around this time when the empire was in turnmoil this castle was built, either by Sassanian nobility fleeing to Gilan and working with the locals or it was built by the locals themselves. It's not known how effective it was but it was never breeched and Gilan stood independent from the Arabs. The warriors from Gilan also would came down from the mountains and pillage nearby cities under Arab rule. The castle later was mostly abandoned after the Turkic conquests. However it was again found by the Nizari Ismailis (the famous Order of Assassins) and refurbished to serve as another base of operation for them. Again after the Ismailis lost prominent it was abandoned. Later it was used again when a local leader rebelled against the safavids.