In ancient Greek religion and mythology, Iacchus (also Iacchos, Iakchos) (Greek: Ἴακχος) was a minor deity, of some cultic importance, particularly at Athens and Eleusis in connection with the Eleusinian mysteries, but of little mythology importance. He perhaps originated as the personification of the ritual exclamation 'Iacche!', cried out during the Eleusinian procession from Athens to Eleusis. He was often identified with Dionysus, perhaps because of the resemblance of the names Iacchus and Bacchus, another name for Dionysus. By various accounts he was a son of Demeter (or apparently her husband), or a son of Persephone, identical with Dionysus Zagreus, or a son of Dionysus.
His name seems to appear in the Linear B (Mycenaean Greek) tablets as i-wa-ko or i-wa-ka. Karl Kerenyi asserts that Iakchos is a Minoan name, propably related with Iakar, a name for Sirius.  Iacchus is related with the verb ἰα^χ-έω (iachéo) meaning "to cry,shout". The verb is also used in Homeric Greek meaning "sound of things".  
Statue, temple, and "feast" day
There was a statue of Iacchus, kept in a temple at Athens. According to the 2nd century AD geographer Pausanias, the statue held a torch and was by the Athenian sculptor Praxiteles. It possibly wore a crown of myrtle, as a passage from Aristophanes' The Frogs suggests. According to Pausanias, the statue was kept in a temple of Demeter located near the Dipylon gate, the main entrance to ancient Athens, and the Pompeion, the building which was the assembly point for the procession celebrating the Eleusinian Mysteries. The temple was perhaps the same temple that Plutarch referred to as the "so called Iaccheion". According to the 10th-century Byzantine encyclopedia the Suda, Iacchus was also the name of his "feast" day.
Iacchus and his statue played an important part in the Eleusinian procession. Plutarch referred to the procession as ἐξαγόντων Ἴακχον (“leading out Iachus”). On 19 Boedromion (around the 27th or 28th of September), the statue of Iacchus, was taken from its temple, and carried as part of the procession of the participants in the Mysteries who walked from Athens to Eleusis. Along the way the participants in the procession would cry out the cultic exclamation ‘’iacche’’.
There was a special official associated with Iacchus and his statue called the ‘’Ἰακχαγωγός’’ ('leader/bearer of Iacchus'), whose function presumably was to carry or accompany the statue of Iacchus during the procession. The ’Ἰακχαγωγός’’ is flisted as one of the Eleusinian officials receiving an endowment c. 160–170 AD, appears in a list of Eleusinian priests given by the 2nd century AD Julius Pollux, and had a reserved seat in the prohedria of the Theater of Dionysus at Athens. An incumbent of the office (126/7 AD) is mentioned on four dedications.
A parody of the Eleusinian procession, appears in Aristophanes' comedy The Frogs, set in Hades, (the underworld). There a chorus of dead mystics, singing and dancing in procession, chant their "hymn to Iacchus": "O Iacchus, Iacchus O!", and sing,
- Iacchus, here abiding in temples most reverend,
- Iacchus, O Iacchus,
- come to dance in this meadow;
- to your holy mystic bands
- Shake the leafy crown
- around your head, brimming
- with myrtle,
- Boldly stomp your feet in time
- to the wild fun-loving rite,
- with full share of the Graces, the holy dance, sacred
- to your mystics.
- Awake, for it has come tossing torches in hand,
- Iacchos, Oh Iacchos,
- the light-bringing star of our nocturnal rite.
- Now the meadow brightly burns
- Old men's knees start to sway.
- They shake away their pains
- and the long cycles of ancient years
- Through your holy rite.
- Beaming with your torch,
- lead forth to the flowering stretch of marsh
- the youth that makes your choruses, o blessed one!
- Now then
- Summon the god of the hour with your songs
- the partner of this dance of ours.
- Iacchus, honored by all, deviser of our festal song
- most sweet, follow us here
- to the goddess and show us how
- you travel a long road with ease.
- Iacchus, lover of the dance, lead me onward,
Iacchus apparently also played a role in the Lenaia, the winter Athenian festival of Dionysus. According to the scholiast on the Frogs of Aristophanes, participants at the Lenaia, responding to the command to "Invoke the god", replied with the invocation: "Hail, Iacchos, son of Semele, thou giver of wealth."
The name Iacchus — identified with Dionysus — was also possibly associated with cultic ritual at Delphi. Sophocles' Antigone, referring nocturnal rites occurring on Mount Parnassus above Delphi, contains the invocation: "O Leader of the chorus of the stars whose breath is fire, overseer of the chants in the night, son begotten of Zeus, appear, my king, with your attendant Thyiads, who in night-long frenzy dance and sing you as Iacchus the Giver!"
Identification with Dionysus
Iacchus became associated with Dionysus by at least the fifth century BC. The association arose perhaps, because of the homophony of the names Iacchus and Bacchus, one of the names of Dionysus. Two black-figure lekythoi (c. 500 BC), represent perhaps, the earliest evidence for such an association. The nearly-identical vases, one in Berlin, the other in Rome, depict Dionysus, along with the inscription IAKXNE, a possible miswriting of IAKXE.
More certain early evidence can be found in the works of the fifth century BC Athenian tragedians Sophocles and Euripides. In Sophocles' Antigone (c. 441 BC), an ode to Dionysus begins by addressing Dionysus as the "God of many names" (πολυώνυμε), who rules over the glens of Demeter's Eleusis, and ends by identifying him with "Iacchus the Giver", who leads "the chorus of the stars whose breath is fire" and whose "attendant Thyiads" dance in "night-long frenzy". And in a fragment from a lost Sophoclean play, Iacchus is also associated with Dionysus: "From here I caught sight of Nysa, haunt of Bacchus, famed among mortals, which Iacchus of the bull's horns counts as his beloved nurse". In Euripides' Bacchae (c. 405 BC), a messenger, describing the Bacchic revelries on mount Cithaeron, associates Iacchus with Bromius, another of the names of Dionysus, saying, they "began to wave the thyrsos ... calling on Iacchus, the son of Zeus, Bromius, with united voice."
An inscription found on a stone stele (c. 340 BC), found at Delphi, contains a paean to Dionysus, which describes the travels of Dionysus to various locations in Greece where he was was honored. From Thebes, where he was born, he first went to Delphi where he displayed his "starry body", and with "Delphian girls" took his "place on the folds of Parnassus", then next to Eleusis, where he is called "Iacchus":
- And in your hand brandishing your night-
- lighting flame, with god-possesed frenzy
- you went to the vales of Eleusis
- where the whole people of Hellas'
- land, alongside your own native witnesses
- of the holy mysteries, calls upon you
- as Iacchus: for mortals from their pains
- you have opened a haven without toils.
The 4th- or 5th-century poet Nonnus describes the Athenian celebrations given to the first Dionysus Zagreus son of Persephone, the second Dionysus Bromios son of Semele, and the third Dionysus Iacchus:
- They [the Athenians] honoured him as a god next after the son of Persephoneia, and after Semele's son; they established sacrifices for Dionysos lateborn and Dionysos first born, and third they chanted a new hymn for Iakkhos. In these three celebrations Athens held high revel; in the dance lately made, the Athenians beat the step in honour of Zagreus and Bromios and Iakkhos all together.
- Graf, s.v. "Iacchus"; Hard, p. 134; Grimal, s.v. "Iacchus", p. 224; Tripp, s.v. "Iacchus", p. 313; Rose, Oxford Classical Dictionary s.v. "Iacchus"; Smith s.v. "Iacchus".
- Compare with Hymenaios, whose name derived from a traditional wedding-cry, see Hard, p. 223.
- Kerényi 1976, p.77
- Jiménez San Cristóbal 2012, p. 125.
- Strabo, 10.3.10; Farnell, p. 146. However Farnell, p. 148, arguing that Iacchus was a late addition to the Eleusinian mysteries, discounts Iacchus as "founder of the mysteries" saying: "if Strabo, in styling [Iacchus] the ἀρχηγέτης τῶν μυστηρίων, means more than that he led the mystae down the saced way to the mystic shrine, we need not be influenced by Strabo against better evidence."
- Jiménez San Cristóbal 2012, pp. 129–130.
- Pausanias, 1.2.4, 1.37.4.
- Aristophanes, Frogs 323–330.
- Plutarch, Aristides 27.3.
- Suda, s.v. Ἴακχος (iota,16); Rose, Oxford Classical Dictionary s.v. "Iacchus"; Harrison, p. 542; Farnell, p. 147.
- Jiménez San Cristóbal 2012, p. 125.
- Plutarch, Themistocles 15.1; Graf, "Iacchus". See also Plutarch, Camillus 19.6, Alcibiades 34.3, Phocion 28.1.
- Plutarch, Themistocles 15.1, Camillus 19.6, Alcibiades 34.3, Phocion 28.1; Graf, "Iacchus"; Farnell, p. 147. Leaving Athens on 19th Boedromion, and arriving in Eleusis on the 20th, are the most likely dates for the procession, see Jiménez San Cristóbal 2012, pp. 125, 129; Kerényi 1991, p. 62; Farnell, p. 147 n. a.
- Athanaassakis and Wolkow, p. 149; Graf, "Iacchus"; Farnell, p. 147; Herodotus, 8.65; Arrian, Anabasis of Alexander 2.16.3. See also Aristophanes, Frogs 316–336, 340–353, 396–404.
- Clinton 1974, p. 96; Farnell, p. 147.
- The "Eleusinian endowment": Inscriptiones Graecae ||2 1092.31.
- Julius Pollux, Onomasticon I 35.
- Inscriptiones Graecae II2 5044.2.
- Inscriptiones Graecae ||2 3733.20–21, 3734.1–3, 4771.11–12, 4772.7–9.
- Guía, p. 110; Athanaassakis and Wolkow, p. 149. Guía suggests that at the Lenaia, Iacchus, in addition to being a young man, and torchbearer, was possibly personified as a child, 'The son of Semele'.
- Farnell, p. 149; Scholiast on Aristophanes, Frogs 482 [= 479 Rutherford]. See also Guía, p. 103; Bowie, A. M., p. 233. According to the scholiast, the command to call on the god, was proclaimed by the Daduchos, a high Eleusinian official.
- Guía, p. 110, which adds the qualification "at least in Attic tragedy".
- Sophocles, Antigone, 1146–1154.
- Jiménez San Cristóbal 2012, p. 125; Bowie, A. M., p. 232; Harrison, pp. 540–542.
- Antikensammlung Berlin F1961 (Beazley Archive 302354).
- National Etruscan Museum 42884, (Beazley Archive 9017720).
- Vernal, pp 32 ff.; Bowie, A. M., p. 232.
- Jiménez San Cristóbal 2012, p. 127.
- Jiménez San Cristóbal 2013, p. 279, Bowie, A. M., p. 232; Sophocles, Antigone 1115–1125, 1146–1154.
- Jiménez San Cristóbal 2013, pp. 279–280; Sophocles, Fragment 959 Radt (Lloyd-Jones, pp. 414, 415).
- Encinas Reguero, p. 350; Jiménez San Cristóbal 2013, p. 282, with n. 41; Euripides, Bacchae 725. Jiménez San Cristóbal also sees possible associations between Iacchus and Dionysus in Euripides: Ion 1074–1086, The Trojan Women 1230, Cyclops 68–71, and fr. 586 Kannicht (apud Strabo, 10.3.13) = fr. 586 Nauck (Collard and Cropp, pp. 56, 57).
- Bowie, E. L., pp. 101–110; Fantuzzi, pp. 189, 190, 191; PHI Greek Inscriptions, BCH 19 (1895) 393.
- 21–24, Bowie, E. L., pp. 101–102.
- 27–35, Bowie, E. L., p. 102.
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