Cista or Cista Mystica
Cista (or cista mystica), a basket used for housing sacred snakes in connection with the initiation ceremony into the cult of Bacchus (Dionysus). In the Dionysian mysteries a serpent, representing the god, was carried in a box called a cista on a bed of vine leaves. This may be the Cista mentioned by Clement of Alexandria which was exhibited as containing the phallus of Dionysus. The cista mentioned in the mysteries of Isis may also have held a serpent, the missing phallus of Osiris. The fertility festival of the women of Arretophoria included cereal paste images ‘of serpents and forms of men,’ in other words, phallic symbols.
Several ancient dignitaries put about the rumour that they had been fathered by a god in serpent form. The emperor Augustus was said to have been fathered by a snake, and his mother never afterwards lost the marks of its embrace. A serpent was said to have been found beside the sleeping Olympias, mother of Alexander the Great. Her husband, Philip of Macedon, is reputed never to have coupled with the 'Bride of the Serpent' again. Alexander is sometimes connected with the horned serpent. The healer god, Asclepios, is said to have fathered a son on a woman who is depicted in Asclepios's temple at Sicyon as sitting on a serpent. Barren women often sought help at the temples of Asclepios to sleep in the precincts of the abaton. So the Idolatry involved is that of fertility, to the land or to the Empire, or Emperor.