Summanus, A Compendium of the Ancient Gods

Where Jupiter cast the thunderbolt by day, Summanus cast it by night. So the Roman priesthood divided the heavens between the two gods, and gave each his own sphere. Summanus was an old Italic deity, much older than the cult of Jupiter Optimus Maximus on the Capitol, and his name was understood by the antiquaries as a contraction of sub-manus, "under the morning," or sub manibus, "the powers below" — the etymology was disputed even in antiquity.

His temple stood near the Circus Maximus, and was struck by a thunderbolt in the year 197 before our era, an ill omen that occasioned much consultation. Pliny records that during this episode the head of a terracotta statue of Summanus was carried off by the river; Cicero, in his De Divinatione, recalls the incident. The remarkable point about Summanus's worship was that his sacrificial cake, called summanalia, was made in the shape of a wheel — a sun-symbol, oddly enough, for a deity of the night-thunder; the cake-shape suggests that Summanus may have once been a sky-god in his own right, surviving as a specialist after Jupiter took the chief place.

By the late Republic, Summanus was little worshipped, and the festival of his temple-foundation on the twentieth of June (Vestalia week) was scarcely observed. Augustine, writing four hundred years later, mentions him only to mock the multiplication of Roman gods: he asks, with some justice, why the Romans needed two thunderbolt-gods when one would do.

Curator’s note

What the sources say, and what later tradition added. The sources for this bay

Summanus is described by Cicero (De Divinatione 1.16, the head-of-statue incident), Pliny (Naturalis Historia 2.138, on lightning lore), Ovid (Fasti 6.731-732), Augustine (City of God 4.23, the mocking passage), and Festus (s.v. Summanalia, on the wheel-cakes). Varro (De Lingua Latina 5.74) records that Titus Tatius the Sabine king brought Summanus's cult to Rome — possibly authentic. Modern scholarship (Bickerman, Dumézil) treats Summanus as a typical example of an archaic specialist deity surviving as a marginal figure under the dominance of the chief sky-god.

When the sources speak

Dated witnesses for The Indigenous Italic Gods. A date marks when the evidence was written down, not when the belief began. The whole timeline

c. 1000–750 BCE: Iron Age communities of Latium and neighboring peoples develop the cult landscapes later absorbed into Roman tradition.
traditional 753 BCE: Roman foundation chronology places Romulus and the first civic institutions at the beginning of the city’s sacred history.
traditional 7th–6th centuries BCE: The regal period is credited with priesthoods, calendars, temples, and the organization of public rites.
509–264 BCE: Republican expansion incorporates Latin, Sabine, Etruscan, and Italian cults through treaty, migration, and evocatio.
264–146 BCE: Mediterranean conquest accelerates Greek interpretation and the importation or redefinition of foreign gods.
204 BCE: The Magna Mater is formally brought from Pessinus during the Second Punic War.
1st century BCE: Varro, Cicero, and other antiquarians document rites and divine names amid civil war and institutional change.
27 BCE–14 CE: Augustan restoration monumentalizes selected ancestral cults and rewrites Roman sacred history.