Aion (Greek Αἰών) is a Hellenistic deity associated with time, the orb or circle encompassing the universe, and the zodiac. The "time" represented by Aion is unbounded, in contrast to Chronos as empirical time divided into past, present, and future. He is thus a god of eternity, associated with mystery religions concerned with the afterlife, such as the mysteries of Cybele, Dionysus, Orpheus, and Mithras. In Latin the concept of the deity may appear as Aevum or Saeculum. He is typically in the company of an earth or mother goddess such as Tellus or Cybele, as on the Parabiago plate.
Iconography and symbolism 
Aion is usually identified as the nude or seminude youth within a circle representing the zodiac, or eternal and cyclical time. Examples include two Roman mosaics from Sentinum (modern–day Sassoferrato) and Hippo Regius in Roman Africa, and the Parabiago plate. But because he represents time as a cycle, he may also be imagined as an old man. In the Dionysiaca, Nonnus associates Aion with the Horae and says that he:
changes the burden of old age like a snake who sloughs off the coils of the useless old scales, rejuvenescing while washing in the swells of the laws [of time].
The imagery of the twining serpent is connected to the hoop or wheel through the ouroboros, a ring formed by a snake holding the tip of its tail in its mouth. The 4th-century AD Latin commentator Servius notes that the image of a snake biting its tail represents the cyclical nature of the year. In his 5th-century work on hieroglyphics, Horapollo makes a further distinction between a serpent that hides its tail under the rest of its body, which represents Aion, and the ouroboros that represents the kosmos, which is the serpent devouring its tail.
Martianus Capella (5th century AD) identified Aion with Cronus (Latin Saturnus), whose name caused him to be theologically conflated with Chronus ("Time"), in the way that the Greek ruler of the underworld Plouton (Pluto) was conflated with Ploutos (Plutus, "Wealth"). Martianus presents Cronus-Aion as the consort of Rhea (Latin Ops) as identified with Physis.
In his highly speculative reconstruction of Mithraic cosmogony, Franz Cumont positioned Aion as Unlimited Time (sometimes represented as the Saeculum, Cronus, or Saturn) as the god who emerged from primordial Chaos, and who in turn generated Heaven and Earth. This deity is represented as the leontocephaline, the winged lion-headed male figure whose nude torso is entwined by a serpent. He typically holds a sceptre, keys, or a thunderbolt. The figure of Time "played a considerable, though to us completely obscure, role" in Mithraic theology.
Aion is identified with Dionysus in Christian and Neoplatonic writers, but there are no references to Dionysus as Aion before the Christian era. Euripides, however, calls Aion the son of Zeus.
The Suda identifies Aion with Osiris. In Ptolemaic Alexandria, at the site of a dream oracle, the Hellenistic syncretic god Serapis was identified as Aion Plutonius. The epithet Plutonius marks functional aspects shared with Pluto, consort of Persephone and ruler of the underworld in the Eleusinian tradition. Epiphanius says that at Alexandria Aion's birth from Kore the Virgin was celebrated January 6: "On this day and at this hour the Virgin gave birth to Aion." The date, which coincides with Epiphany, brought new year's celebrations to a close, completing the cycle of time that Aion embodies. The Alexandrian Aion may be a form of Osiris-Dionysus, reborn annually. His image was marked with crosses on his hands, knees, and forehead. Gilles Quispel conjectured that the figure resulted from integrating the Orphic Phanes, who like Aion is associated with a coiling serpent, into Mithraic religion at Alexandria, and that he "assures the eternity of the city."
Roman Empire 
This syncretic Aion became a symbol and guarantor of the perpetuity of Roman rule, and emperors such as Antoninus Pius issued coins with the legend Aion, whose female Roman counterpart was Aeternitas. Roman coins associate both Aion and Aeternitas with the phoenix as a symbol of rebirth and cyclical renewal.
Aion was among the virtues and divine personifications that were part of late Hellenic discourse, in which they figure as "creative agents in grand cosmological schemes." The significance of Aion lies in his malleability: he is a "fluid conception" through which various ideas about time and divinity converge in the Hellenistic era, in the context of monotheistic tendencies.
See also 
- Doro Levi, "Aion," Hesperia 13.4 (1944), p. 274.
- Levi, "Aion," p. 274.
- Levi, "Aion," p.
- Nonnus, Dionysiaca 41.180ff., as cited by Levi, "Aion," p. 306.
- Servius, note to Aeneid 5.85, says that "according to the Egyptians, before the invention of the alphabet the year was symbolized by a picture, a serpent biting its own tail, because it recurs on itself" (annus secundum Aegyptios indicabatur ante inventas litteras picto dracone caudam suam mordente, quia in se recurrit), as cited by Danuta Shanzer, A Philosophical and Literary Commentary on Martianus Capella's De Nuptiis Philologiae et Mercurii Book 1 (University of California Press, 1986), p. 159.
- Horapollo, Hieroglyphica 1.1 and 1.2 in the 1940 edition of Sbordone, as cited by Shanzer, A Philosophical and Literary Commentary on Martianus Capella, p. 154.
- Schanzer, A Philosophical and Literary Commentary on Martianus Capella, p. 137.
- Summarized by Jaime Alvar Ezquerra, Romanising Oriental Gods: Myth, Salvation, and Ethics in the Cults of Cybele (Brill, 2008), p. 78.
- Ezquerra, Romanising Oriental Gods, p. 128.
- Guthrie, W.K.C. (1979). A history of Greek philosophy: The earlier presocratics and the Pythagoreans. Cambridge University Press,. p. 478. ISBN 978-0-521-29420-1.
- Euripides, Heracleidae 899f.
- Pseudo-Callisthenes, I.30–33, as cited by Jarl Fossum, "The Myth of the Eternal Rebirth: Critical Notes on G.W. Bowersock, Hellenism in Late Antiquity," Vigiliae Christianae 53.3 (1999), p. 309, note 15. On the oracle and for the passage in which Aion Plutonius is named, see Irad Malkin, Religion and Colonization in Ancient Greece (Brill, 1987), p. 107, especially note 87.
- Fossum, "The Myth of the Eternal Rebirth," pp. 306–307.
- Gilles Quispel, "Hermann Hesse and Gnosis," in Gnostica, Judaica, Catholica: Collected Essays (Brill, 2008), p. 258; Gary Forsythe, Time in Roman Religion: One Thousand Years of Religious History (Routledge, 2012), p. 122.
- Fossum, "The Myth of the Eternal Rebirth," p. 309.
- Fossum, "The Myth of the Eternal Rebirth," pp. 306–307, 311.
- Quispel, "Hermann Hesse and Gnosis," p. 258.
- Fossum, "The Myth of the Eternal Rebirth," p. 314.
- Ittai Gradel, Emperor Worship and Roman Religion (Oxford University Press, 2002), pp. 310–311.
- Levi, "Aion," pp. 307–308.
- J. Rufus Fears, "The Cult of Virtues and Roman Imperial Ideology," Aufstieg und Niedergang der römischen Welt II.17.2 (1981), p. 939.
- Levi, "Aion," pp. 307–308 et passim.