Cista or Cista Mystica
The cista (or cista mystica) was 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 cista on a bed of vine leaves. Clement of Alexandria wrote of a cista which was exhibited as containing the phallus of Dionysus. The cista mentioned in the mysteries of Isis may also have held a serpent, representing the missing phallus of Osiris.
ancient dignitaries put about the rumor 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' 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.