Dius Fidius

In ancient Roman religion, Dius Fidius (less often as Dius Fidus) was a god of oaths associated with Jupiter. His name was thought to be related to Fides.

Fidius may be an earlier form for filius, "son", with the name Dius Fidius originally referring to Hercules as a son of Jupiter. According to some writers, the phrase medius fidius was equivalent to mehercule "My Hercules!", a common interjection.

Varro states that his teacher Aelius Stilo called this god Diovis filium, i.e. Dius Filius as the Greek Διόσκορον Castorem on the grounds of the alteration of the letters d and l in the Sabine tongue. He identified him in Sabine, Sancus and in Greek, Hercules. This assumption is not linguistically correct, because in the Iguvine Tables the god is named Fis(i)us or Fisovius Sancius. However, his intrepretation, based on unknown theological documents, tallies with that of some modern scholars. The god is certainly not a mere aspect of Jupiter but a separate entity, known in Rome as Semo Sancus Dius Fidius. Wissowa argues that Jupiter and Dius Fidius divide responsibility for ensuring good faith. The most important oaths are sworn by Jupiter, the god of the Fides Publica Populi Romani as Iuppiter Lapis. Dius Fidius protects good faith in private affairs: he corresponds to Ζευς Πίστιος. This view may well reflect a later development but is not the original interpretation. Dius Fidius was not confined to private fides in early times. Matters of public relevance (such as the first international treaty of Rome, the one with Gabii) were preserved in his shrine (put under his jurisdiction).

The shrine of Sancus had no roof, as it was deemed inappropriate and ineffective to swear oaths unless under the sky. The Capitoline temple also had an opening in its roof.

The association of Dius Fidius with Jupiter is divine filiation. Dumézil underlines the peculiar intertwining and mixing of Jupiter and Dius Fidius as wardens of oaths and wielders of lightning bolts. Both require an opening in the roof of their temples while leaving unanswered for Dumézil the question of the true identity of the latter.

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