The Panhellenic sanctuary of Delphi, primarily dedicated to Apollo, welcomed Dionysos during the months of winter and early spring, when Apollo was said to be visiting the Hyperboreans. Delphic theology emphasized an intimate fraternal relationship between the two deities. Excavation of the Sacred Way brought to light a stele inscribed in 340/339 with a paian in which Dionysos is urged to appear “in the holy season of spring” for the Theoxenia (Hospitality to the Gods), a festival at which deities were provided with food, drink, and entertainment.26 It also describes major additions to Dionysos’ Delphic cult: the establishment of a sacrifice and dithyrambic competition, the erection of a statue of Bakchos “in a chariot drawn by golden lions” and the building of a grotto “suitable for the holy god.”
Already in the fifth century, tragedians speak of the ecstatic worship of Dionysos high on the slopes of Mt. Parnassos. Here the entourage of Dionysos, whether mortal women or nymphs, were called Thyiads (Raving Ones), and they are described as scaling the twin peaks above the Korykian cave, roving over the mountain with torches to light their way and wetting the rocks with sacrificial blood.27 No special altar or cult place is mentioned either on the mountain or in the sanctuary itself, though by the fourth century Dionysos and some rather sedate Thyiads, whose fragmentary remains have been recovered, were sculpted in the west pediment of Apollo’s new temple. Like other mainadic festivals, this one took place every other winter; the Thyiads must have experienced great dangers and discomforts on the cold, dark slopes of Parnassos. It would be difficult to believe that Greek women actually danced on the mountain at night, were it not for the testimony of Plutarch (Mor. 249e-f, 953d), who served as a priest at Delphi during the turn of the first century CE. In his day, the Thyiads once had to be rescued when they were caught in a snowstorm on Parnassos. Pausanias (10.4.3) reports that he spoke with Thyiads from Attica, who joined with their Delphic counterparts every other year to perform mysterious rites for Dionysos.