Si deus si dea
Si deus si dea is an Archaic Latin phrase meaning "whether god or goddess", used to address a deity of unknown gender. It was also written sive deus sive dea, sei deus sei dea, or sive mas sive femina ("whether male or female").
The phrase can be found on several ancient monuments. Archaic Roman inscriptions such as this might have written to protect the identity of the god if Rome were ever captured by an enemy. The construction was often used when invoking the god of a place (e.g., "Be you god or goddess who reigns over Carthage, grant us..."). Historian Edward Courtney believes it was "intended to cover all bases as an acknowledgement of the limitations of human knowledge about divine powers," similar to the Greek Unknown God.
Altar to the Unknown Divinity 
which can be transliterated into the modern alphabet as
- Sei deo sei deivae sac(r + dative case ending o [masc.] / ae [fem.])
- G(aius) Sextius C(aii) f(ilius) Calvinus pr(aetor)
- de senati sententia
and translated as
- Whether to a god or goddess sacred,
- Caius Sextius Calvinus, son of Caius, praetor
- by order of the Senate
- restored this.
The altar has been dated as a late Roman Republic restoration of an Archaic original. In the 19th century it was misidentified as a famous altar to Aius Locutius, but the real identity of the divinity cannot be known, as it is not even specified whether it is a god or a goddess. The praetor Caius Sextius C.f. Calvinus may have restored an earlier altar reading "sei deo sei deivae" for the reasons described above, or he may have been restoring an altar which had been forgotten and left to decay, and the god or goddess it was dedicated to was no longer remembered by any Roman.
Ferter Resius 
Close to the site, four inscribed columns were found dating to the Julio-Claudian period. Column A (now missing) read "Marspiter," or "Father Mars" in Archaic Latin. Column B reads "Remureine," which possibly means "In Memory of Remus." Column C reads "anabestas," possibly a goddess named Anabesta, or else related to the Greek anabasio ("to go up") and interpreted as a reference to Remus' scaling of the Roman walls. Column D, the longest inscription, reads:
- Ferter Resius / rex Aequeicolus / is preimus / ius fetiale paravit / inde p(opulus) R(omanus) discipleinam excepit.
Livy ascribes the institution of the fetiales to Ancus Marcius, and claims that the ius fetiale came to Rome by the Aequicoli.
- Description of the Altar to the Unknown Divinity, found at the Palatine Hill Museum.
- De Numinibus, essay by Mauk Haemers
- Sandys, Sir John Edwin (1919). Latin epigraphy: an introduction to the study of Latin inscriptions. Cambridge: Cambridge University Press. p. 89.
- Description of the altar at University of Texas at Austin' Digital Archive Services
- Rodolfo Lanciani, Pagan and Christian Rome, 1892
- Internet Archive: Details: Thesaurus linguae latinae epigraphicae [microform] ; a dictionary of the Latin inscriptions
- Livy, Ab Urbe Condita, 1.32.5
Further reading 
- Alvar, Jaime, 1988: "Materiaux pour l'etude de la formule sive deus, sive dea" Numen 32,2, 236-273.