They represented four of the asteroids in the Solar System's asteroid belt that were at one point in time classified as planets. Their names were Sailor Ceres (pink), Sailor Pallas (blue), Sailor Juno (green), and Sailor Vesta (red). While they waited for Sailor Chibi Moon to take on her role, they slept in the Amazon stones.
They were prematurely awakened from their stones in the Dream Arc of the manga by the Dead Moon Circus and recruited as the villainesses CereCere, PallaPalla, JunJun, and VesVes (the Amazoness Quartet). After their defeat they revert to their stones, Sailor Saturn gathers the stones and gave them to Neo-Queen Serenity. In the manga, after the Dead Moon was defeated, their true Senshi forms were revealed. In the anime, the Amazoness Quartet appeared in the Sailor Moon SuperS season but did not become Senshi.