Gerdkuh

Iran, Iran

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Gerdkuh (also spelled Gerd‑kuh or Dezh‑e Gonbadān, meaning “fortress of the domes”) is a major medieval mountain fortress located about 17–18 kilometers west of Damghan in the Alborz mountains of modern Semnan Province, Iran, on an isolated, roughly circular rocky hill that rises about 300 meters above the surrounding ground.

The name “Gerdkuh” comes from the Persian words “gerd” (round) and “kuh” (mountain), reflecting the circular shape of the hill’s summit, and the castle is famous for its triple ring of concentric fortifications at the base, which made it appear almost impregnable to attackers.

Although the site may have pre‑Islamic origins, its first recorded history dates to the 10th century CE, when it became an Isma’ili stronghold; by the 11th century it was under Seljuk control, and from the late 11th century until the Mongol conquest it formed part of the Nizari Isma’ili state, serving as a refuge for the families of leaders such as Hasan Sabbah.