When Ceres became associated with the plebs in 500 BCE, that association was tied with the foundation of a new temple on the Aventine hill devoted to her, Liber, and Libera in association. This temple because a focal point for plebeian class consciousness and political organization in the early Republic. The plebeian magistrates, the tribunes and aediles, were closely associated with Ceres, and the aediles served as priests in the Aventine Triad's cult (Spaeth 6). The Triad's temple directly faced the Circus Maximus and stood outside the pomerium, the sacred boundary of the city. Since only native Roman cults were allowed inside the pomerium, this may mark the Triad as being perceived as somehow foreign, perhaps because of its assumption of the southern Greek mythology associated with Demeter, Bacchus, and Kore (Beard 65). However, the association of Bacchus with Kore and Demeter was not common (Spaeth 378). The new Triadic cult was associated with the much older cult of Ceres by herself and formally assumed all of its functions (7), with a new emphasis on protecting the urban grain supply. The Aventine Triad, as it was initially created, was the plebeian counterpart of the Capitoline Triad of Jupiter, Juno, and Minerva. It was allegedly created as the result of a consultation of the Sibylline Books (Dumezil 89).
The Triadic cult synthesized several other older traditions relating to the individual deities together. Liber and Libera were likely a dyad of a sort that dominated early Roman religion, which also featured pairs of deities like Faunus and Fauna. Liber and Libera together probably presided specifically over human sexual union before being associated with Ceres in the Triad (8).
As time passed and the individual deities assimilated more mythology, their portrayals grew more complex. A cameo dated to the imperial period portrays Ceres standing, holding stalks of grain in her right hand; to the center is Libera in her guise as Prosperpina, who is handing the newborn child Liber in his guise as Iacchos (Bacchus) to the birth goddess Eileithyia. It is possible that the Triad together played a role in the Eleusinian Mysteries. Ceres appears alongside Proserpina and Iacchos in scenes that seem to reflect details of the initiation in the mysteries (27).
