Caelus or Coelus was a primal god of the sky in Roman myth and theology, iconography, and literature (compare caelum, the Latin word for "sky" or "the heavens", hence English "celestial"). The deity's name usually appears in masculine grammatical form when he is conceived of as a male generative force, but the neuter form Caelum is also found as a divine personification.
The name of Caelus indicates that he was the Roman counterpart of the Greek god Uranus (Οὐρανός, Ouranos), who was of major importance in the theogonies of the Greeks. Varro couples him with Terra (Earth) as pater and mater (father and mother), and says that they are "great deities" (dei magni) in the theology of the mysteries at Samothrace. Although Caelus is not known to have had a cult at Rome, not all scholars consider him a Greek import given a Latin name; he has been associated with Summanus, the god of nocturnal thunder, as "purely Roman."
Caelus begins to appear regularly in Augustan art and in connection with the cult of Mithras during the Imperial era. Vitruvius includes him among celestial gods whose temple-buildings (aedes) should be built open to the sky. As a sky god, he became identified with Jupiter, as indicated by an inscription that reads Optimus Maximus Caelus Aeternus Iup<pi>ter.
According to Cicero and Hyginus, Caelus was the son of Aether and Dies ("Day" or "Daylight"). Caelus and Dies were in this tradition the parents of Mercury. Caelus was the father with Hecate of the distinctively Roman god Janus, as well as of Saturn and Ops. Caelus was also the father of one of the three forms of Jupiter, the other two fathers being Aether and Saturn. In one tradition, Caelus was the father with Tellus of the Muses, though was this probably a mere translation of Ouranos from a Greek source.
Myth and allegory 
Caelus substituted for Uranus in Latin versions of the myth of Saturn (Cronus) castrating his heavenly father, from whose severed genitals, cast upon the sea, the goddess Venus (Aphrodite) was born. In his work On the Nature of the Gods, Cicero presents a Stoic allegory of the myth in which the castration signifies "that the highest heavenly aether, that seed-fire which generates all things, did not require the equivalent of human genitals to proceed in its generative work." For Macrobius, the severing marks off Chaos from fixed and measured Time (Saturn) as determined by the revolving Heavens (Caelum). The semina rerum ("seeds" of things that exist physically) come from Caelum and are the elements which create the world.
The divine spatial abstraction Caelum is a synonym for Olympus as a metaphorical heavenly abode of the divine, both identified with and distinguished from the mountain in ancient Greece named as the home of the gods. Varro says that the Greeks call Caelum (or Caelus) "Olympus." As a representation of space, Caelum is one of the components of the mundus, the "world" or cosmos, along with terra (earth), mare (sea), and aer (air). In his work on the cosmological systems of antiquity, the Dutch Renaissance humanist Gerardus Vossius deals extensively with Caelus and his duality as both a god and a place that the other gods inhabit.
The ante-Nicene Christian writer Lactantius routinely uses the Latin theonyms Caelus, Saturn, and Jupiter to refer to the three divine hypostases of the Neoplatonic school of Plotinus: the First God (Caelus), Intellect (Saturn), and Soul, son of the Intelligible (Jupiter).
In art 
It is generally though not universally agreed that Caelus is depicted on the cuirass of the Augustus of Prima Porta, at the very top above the four horses of the Sun god's quadriga. He is a mature, bearded man who holds a cloak over his head so that it billows in the form of an arch, a conventional sign of deity (velificatio) that "recalls the vault of the firmament." He is balanced and paired with the personification of Earth at the bottom of the cuirass. (These two figures have also been identified as Saturn and the Magna Mater, to represent the new Saturnian "Golden Age" of Augustan ideology.) On an altar of the Lares now held by the Vatican, Caelus in his chariot appears along with Apollo-Sol above the figure of Augustus.
Nocturnus and the templum 
As Caelus Nocturnus, he was the god of the night-time, starry sky. In a passage from Plautus, Nocturnus is regarded as the opposite of Sol, the Sun god. Nocturnus appears in several inscriptions found in Dalmatia and Italy, in the company of other deities who are found also in the cosmological schema of Martianus Capella, based on the Etruscan tradition. In the Etruscan discipline of divination, Caelus Nocturnus was placed in the sunless north opposite Sol to represent the polar extremities of the axis (see cardo). This alignment was fundamental to the drawing of a templum (sacred space) for the practice of augury.
Mithraic Caelus 
The name Caelus occurs in dedicatory inscriptions in connection to the cult of Mithras. The Mithraic deity Caelus is sometimes depicted allegorically as an eagle bending over the sphere of heaven marked with symbols of the planets or the zodiac. In a Mithraic context he is associated with Cautes and can appear as Caelus Aeternus ("Eternal Sky"). A form of Ahura-Mazda is invoked in Latin as Caelus Aeternus Iupiter. The walls of some mithrea feature allegorical depictions of the cosmos with Oceanus and Caelus. The mithraeum of Dieburg represents the tripartite world with Caelus, Oceanus, and Tellus below Phaeton-Heliodromus.
As the Jewish god 
Some Roman writers used Caelus or Caelum as a way to express the monotheistic god of Judaism. Juvenal identifies the Jewish god with Caelus as the highest heaven (summum caelum), saying that Jews worship the numen of Caelus; Petronius uses similar language. Florus has a rather odd passage describing the Holy of Holies in the Temple of Jerusalem as housing a "sky" (caelum) under a golden vine, which has been taken as an uncomprehending attempt to grasp the presence of the Jewish god. A golden vine, perhaps the one mentioned, was sent by the Hasmonean king Aristobulus to Pompeius Magnus after his defeat of Jerusalem, and was later displayed in the Temple of Jupiter Capitolinus.
- Neuter, for instance, at Varro, De lingua latina 5.57, where a masculine form might be expected for the partner of Terra. Neuter also at Hyginus, Fabula pr. 2 (17) in a series of divine personifications with Terra and Mare (the Sea). The masculine and neuter forms of the name Caelus and Caelum differ only in the vocative and nominative cases; when a second-declension noun appears in the genitive, dative, or ablative case, there is no way to distinguish whether the neuter or masculine is meant. When the deity is conceived of as plural, "the Heavens," the masculine Caeli is used, and not the neuter Caela, which would create an ambiguity with first-declension nouns of feminine gender. Divine personifications in Latin are mostly feminine.
- Varro, De lingua Latina 5.58.
- Pierre Grimal, The Dictionary of Classical Mythology (Blackwell, 1986, 1996, originally published 1951 in French), pp. 83–84.
- Marion Lawrence, "The Velletri Sarcophagus," American Journal of Archaeology 69.3 (1965), p. 220.
- Other gods for whom this aedes design was appropriate are Jupiter, Sol and Luna. Vitruvius, De architectura 1.2.5; John E. Stambaugh, "The Functions of Roman Temples," Aufstieg und Niedergang der römischen Welt II.16.1 (1978), p. 561.
- CIL 6.81.2.
- Cicero, De natura deorum 3.44, as cited by E.J. Kenney, Apuleius: Cupid and Psyche (Cambridge University Press, 1990, 2001), note to 6.6.4, p. 198; Hyginus, preface. This is not the theogony that Hesiod presents.
- Cicero, De natura Deorum 3.56; also Arnobius, Adversus Nationes 4.14.
- Ennius, Annales 27 (edition of Vahlen); Varro, as cited by Nonius Marcellus, p. 197M; Cicero, Timaeus XI; Arnobius, Adversus Nationes 2.71, 3.29.
- Arnobius, Adversus Nationes 4.14.
- Arnobius, Adversus Nationes 3.37, citing Mnaseas as his source.
- Cicero, De nature Deorum; Arnobius, Adversus Nationes 4.24.
- Cicero, De natura Deorum 2.64. Isidore of Seville says similarly that Saturn "cut off the genitalia of his father Caelus, because nothing is born in the heavens from seeds" (Etymologies 9.11.32). Jane Chance, Medieval Mythography: From Roman North Africa to the School of Chartres, A.D. 433–1177 (University Press of Florida, 1994), pp. 27 and 142.
- Macrobius, Saturnalia 1.8.6–9; Chance, Medieval Mythography, p. 72.
- Varro, De lingua latina 7.20; likewise Isidore of Seville, Etymologies 14.8.9. The noun Caelum appears in the accusative case, which obscures any distinction between masculine and neuter. Servius, note to Aeneid 6.268, says that "Olympus" is the name for both the Macedonian mountain and for caelum. Citations and discussion by Michel Huhm, "Le mundus et le Comitium: Repésentations symboliques de l'espace de la cité," Histoire urbaine 10 (2004), p. 54.
- Servius, note to Aeneid 3.134; Huhm, "Le mundus et le Comitium," p. 53, notes 36 and 37.
- Gerardus Vossius, Idolatriae 3.59 online et passim, in Gerardi Joan. Vossii Operum, vol. 5, De idololatria gentili. See also Giovanni Santinello and Francesco Bottin, Models of the History of Philosophy: From Its Origins in the Renaissance to the "Historia Philosophica" (Kluwer, 1993), vol. 1, pp. 222–235.
- Elizabeth De Palma Digeser, "Religion, Law and the Roman Polity: The Era of the Great Persecution," in Religion and Law in Classical and Christian Rome (Franz Steiner, 2006), pp. 78–79.
- Jane Clark Reeder, "The Statue of Augustus from Prima Porta, the Underground Complex, and the Omen of the Gallina Alba," American Journal of Philology 118.1 (1997), p. 109; Charles Brian Rose, "The Parthians in Augustan Rome," American Journal of Archaeology 109.1 (2005), p. 27.
- Karl Galinsky, Augustan Culture: An Interpretive Introduction (Princeton University Press, 1996), pp. 158 and 321.
- Reeder, "The Statue of Augustus," p. 109.
- Specifically, Juppiter Optimus Maximus Saturnus Augustus: Reeder, "The Statue of Augustus," p. 109 and 111.
- Reeder, "The Statue of Augustus," p. 103; Lily Ross Taylor, "The Mother of the Lares," American Journal of Archaeology 29.3 (1925), p. 308.
- Plautus, Amphytrion 272.
- Including CIL 3.1956 = ILS 4887, 9753, 142432, CIL 5.4287 = ILS 4888, as cited and discussed by Mario Torelli, Studies in the Romanization of Italy (University of Alberta Press, 1995), pp. 108–109.
- Torelli, Studies, p. 110. See also Huhm, "Le mundus et le Comitium," pp. 52–53, on the relation of templum, mundus, and caelum.
- Doro Levi, "Aion," Hesperia (1944), p. 302.
- M.J. Vermaseren, Mithraica I: The Mithraeum at S. Maria Capua Vetere (Brill, 1971), p. 14; Jaime Alvar, Romanising Oriental Gods: Myth, Salvation, and Ethics in the Cults of Cybele, Isis, and Mithras, translated by Richard Gordon (Brill, 2008), p. 86.
- R. Beck in response to I.P. Culianu, "L'«Ascension de l'Âme» dans les mystères et hors des mystères," in La Soteriologia dei culti orientali nell' impero romano (Brill, 1982), p. 302.
- Levi, "Aion," p. 302. This was the view also of Salomon Reinach, Orpheus: A General History of Religions, translated by Florence Simmonds (London: Heinemann, 1909), p. 68.
- Vermaseren, Mithraica I, p. 14.
- The word does not appear in the nominative case in any of the passages, and so its intended gender cannot be distinguished; see above.
- Juvenal, Satires 14.97; Peter Schäfer, Judeophobia: Attitudes toward the Jews in the Ancient World (Harvard University Press, 1997), pp. 41, 79–80.
- Petronius, frg. 37.2; Schäfer, Judeophobia, pp. 77–78.
- Florus, Epitome 1.40 (3.5.30): "The Jews tried to defend Jerusalem; but he [Pompeius Magnus] entered this city also and saw that grand Holy of Holies of an impious people exposed, Caelum under a golden vine" (Hierosolymam defendere temptavere Iudaei; verum haec quoque et intravit et vidit illud grande inpiae gentis arcanum patens, sub aurea vite Caelum). Finbarr Barry Flood, The Great Mosque of Damascus: Studies on the Makings of an Umayyad Visual Culture (Brill, 2001), pp. 81 and 83 (note 118). The Oxford Latin Dictionary (Oxford: Clarendon Press, 1982, 1985 reprinting), p. 252, entry on caelum, cites Juvenal, Petronius, and Florus as examples of Caelus or Caelum "with reference to Jehovah; also, to some symbolization of Jehovah."