In contrast to Jupiter, who was the god of diurnal (daytime) thunder, Summanus was the deity of nocturnal thunder. Even to Ovid, his exact nature was unknown.
One of the nine thunder gods, according to Pliny, was of Etruscan descent. However, King Titus Tatius consecrated altars (arae) to Summanus as the result of a votum, who Varro believes to be a Sabine deity. He is worshipped as a deity of lightning by Paulus Diaconus. Summanus is another name for Pluto, which Martianus Capella describes as the “highest” (summus) of the Manes. This comparison is made by subsequent authors like Cames (“If in Summanus’ gloomy realm / Severest punishment you now endure …”) and Milton, in a simile to describe Satan visiting Rome: “Just so Summanus, wrapped in a smoking whirlwind of blue flame, falls upon people and cities”.
According to Georges Dumézil, Summanus would stand in for the terrifying, terrible, and awe-inspiring aspect of the gods of the first function, which is associated with celestial supremacy. The dichotomy Varuna-Mitra in Vedic religion and Summanus-Dius Fidius in Roman religion both represent the dual nature of celestial sovereign authority. While the second gods of these pairings would represent sovereignty’s comforting, daytime, and juridical aspects, the first gods of these pairs would represent its violent, nocturnal, mysterious side.
Weird Italy, Guide to Unusual & Amazing Places to see in Italy. Italy’s news in English: Art, History & Facts