Janus Bifrons. This was an appelation assigned to Janus, because he was represented with two faces, in consideration, as Servius states, of the alliance made between the Romans and the Sabines. Also, perhaps, according to other writers, to signify he knew both the past and the future.
The as, the most ancient coin of the Romans, bears on one side the head of Janus with two faces, bearded, and above it a crescent, symbol of enternity; on the reverse, we see the prow of the ship which brought Saturn to Italy: a type which has caused this coinage of brass money to be called ratti, from the Latin word ratis, a ship or galley. These pieces are common in numismatic cabinets.
The half-naked figure of two-headed Janus, standing with a spear in his right hand, on a first brass medal of Antoninus Pius, indicates either some sacred honours paid to Janus by that Emperor; or that the sercurity of the age was established by the providential care of Antoninus, as formerly under the reign of Janus. The legend of this coin is TR POT COS III, which Eckhel gives to VC 893.
There is a brass medallion of Commodus, which exhibits on its reverse the head of Janus, one of the faces having the likeness of that Emperor: the epigraph which accompanies it is TR P XII IMP VIII COS V PP See also the TELLVS STABIL of COMMODVS on a brass medallion.
There are other medallions of Commodus, which all present the figure of the double Janus, and are remarkable for their elegence and rarity though the reason for the selection of such a type remains unknown. -This adoration of Janus on the |part| of Commodus, appears to have been an exemplification of that Pietas of which we see him styled the Auctor. The excess of his prediliction for Janus is manifested by a coin of the Medicean collection, on the obverse of which the head of Commodus is represented with double face, like that of the God. -D. N. Vet. vii., 119.
The head of Janus, with its beardless faces, after the likeness of Cnæius Pompeius (Pompey the Great) appears on the obverse of |Pompey 's| first brass, and the prow of a ship on the reverse.
Janus is said to have had a son, named Fontus, from whom the Fonteii assumed to derive their origin, and their right to place the head of Janus on their coins. See Fonteia.