The Ancient Stronghold was a fort in the Green City on the island of Lemnos, Greece. Once a fort occupied by the military, it had been abandoned by the time the Cult of Kosmos found the place. The Cult, notably the cultist Iobates the Stoic, occupied the fort, stationing a sizeable force there.
During the Peloponnesian War, the Spartan misthios Kassandra following a scytale decoded by her late friend Phidias, explored the place and discovered a hidden back room containing treasures. She also assassinated Iobates and the cultist general in order to stop their kidnappings and poisoning of the villagers.