The Great Mothers' Fortress served as the lair of the witches Klothow, Aktropaw, and Lakesis, the Great Mothers of Peridea. Later, Grand Admiral Mitth'raw'nuruodo found the fortress and awoke the mothers within, after being exiled from his home galaxy during the Liberation of Lothal. He made an alliance with them, utilizing their magick to repair his Star Destroyer, the Chimaera, and to contact one of his agents in the main galaxy. In return, Thrawn would take the mothers and their cargo with him.
After traveling through extragalactic hyperspace, Thrawn's agent, Morgan Elsbeth arrived above Peridea aboard the Eye of Sion, intended to ferry Thrawn and the Great Mothers to Dathomir. She and her mercenaries arrived at the fortress and were greeted by the mothers. Soon afterward, the Chimaera docked over the fortress and began transferring the cargo onboard. Thrawn orchestrated the efforts to use Sabine Wren to find and kill Ezra Bridger from here as well as the interception of Ahsoka Tano. Although the Jedi survived, the cargo transfer was completed and preparations for departure were begun. Tano, Wren, and Bridger infiltrated the fortress to prevent it, but Morgan stayed behind to buy Thrawn and the Mothers more time, long enough to leave the fortress.
In an effort to halt the Jedi's advance, Thrawn ordered the Chimaera's turbolasers to fire on the fortress, noticeably upsetting the Great Mothers. Tano and Wren narrowly escaped, but the reanimated Night Troopers were destroyed when it crumbled.