Essence cages were an invention of the magician Khaba the Cruel. Within them, he would trap spirits using the spell of Indefinite Confinement, a form of dismissal that nevertheless trapped the spirit within a prison on Earth. The cages were reinforced with force lines to keep the spirits trapped and docile. The essence cages were destroyed by Bartimaeus of Uruk when, he, in a rage, rampaged them before being trapped in a bottle by the marid Ammet, also using the spell of Indefinite Confinement.