The cave of the ancients was the name given to a specific tunnel beneath the fortress with no name, at the heart of the glittering plain. Centuries before the events of the contemporary Annals, numerous mysterious men (the "ancients") were placed in the cave, where they were encrusted with magic ice, and kept alive, but unconscious, in stasis.
Touching a person in stasis would disrupt the protection spells that manifested as the frosty webs, killing them.
Soulcatcher took advantage of the cave to freeze many of her enemies, including her hated sister Lady and several other veterans, allies, and prisoners of the Black Company. With the help of Willow Swan (whom she seduced with her sorcery), she disabled them and placed them in the cave at the end of She Is the Darkness. They remained there for 15 years. They would come to be identified as "the Captured" by Sleepy, who dedicated her life to rescuing them. One of the Captured was even a fellow member of the Ten Who Were Taken, the Howler. Soulcatcher took great care not to touch the frozen ancients in the cave while installing her enemies. Later, when Sleepy and her band finally freed the Captured at the end of Water Sleeps, she also took similar care not to disturb the ancients.