Dius Fidius, then, and Semo Sancus are both Latin names for the same religious conception, the impersonality of which caused it to lose vitality as new and anthropomorphic ideas of the divine came into vogue at Rome. But there is at least some probability that it survived in a fashion under the name of an intruder, Hercules; and the connexion with Hercules will show, what we might already have guessed, that the religious conception we are speaking of was very near akin to that of Jupiter himself.
There is clear evidence that the best Roman scholars identified not only Dius Fidius with Semo Sancus, but both of these with Hercules. Varro, in a passage already quoted, tells us that Stilo believed Dius Fidius to be the Sabine Sancus and the Greek Hercules; Verrius Flaccus, if his excerptors represent him rightly, in two separate glosses identified all these three[555].
Again, the Roman oaths _me dius fidius_ and _me hercule_ are synonymous; that the former was the older can hardly be doubted, and the latter must have come into vogue when the Greek oath by Heracles became familiar. Thus the origin of _me hercule_ must be found in a union of the characteristics of Hercules with those of the native Dius Fidius. It is worth noting that in pronouncing both these oaths it was the custom to go out into the open air[556]. Here is a point at which both Hercules and Dius Fidius seem to come into line with Jupiter; for the most solemn oath of all was _per Iovem_ (_lapidem_), also taken under the light of heaven[557], as was the case with the oath at the altar of Ζεὺς Ἑρκεῖος in Greece[558]. Yet another point of conjunction is the _ara maxima_ at the entrance to the Circus Maximus, which was also a place where oaths were taken and treaties ratified[559]; this was the altar of Hercules Victor, to whom the tithes of spoil were offered; and this was also associated with the legend of Hercules and Cacus. In the deity by whom oaths were sworn, and in the deity of the tithes and the legend, it is now acknowledged on all hands that we should recognize a great Power whom we may call Dius Fidius, or Semo Sancus, or the Genius Iovius, or even Jupiter himself[560]. Tithes, oaths, and the myth of the struggle of light with darkness, cannot be associated with such a figure as the Hercules who came to Italy from Greece; tithes are the due of some great god, or lord of the land[561], oaths are taken in the presence of the god of heaven, and the great nature myth only descends by degrees to attach itself to semi-human figures.