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.

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).