This stems from the earlier question I posted on 1 October 2013, for a friend seeking the source of a reference to these in a medieval translation of Boethius. Please see that question for more details.
19 Regionem istam, quae nunc vocatur Italia, regno Ianus optinuit, qui, ut Hyginus Protarchum Trallianum secutus tradit, cum Camese aeque indigena terram hanc ita participata potentia possidebant, ut regio Camesene, oppidum Ianiculum vocitaretur. 20 Post ad Ianum solum regnum redactum est, qui creditur geminam faciem praetulisse, ut quae ante quaeque post tergum essent intueretur: quod procul dubio p52ad prudentiam regis sollertiamque referendum est, qui et praeterita nosset et futura prospiceret, sicut Antevorta et Postvorta, divinitatis scilicet aptissimae comites, apud Romanos coluntur. 21 Hic igitur Ianus, cum Saturnum classe pervectum excepisset hospitio et ab eo edoctus peritiam ruris ferum illum et rudem ante fruges cognitas victum in melius redegisset, regni eum societate muneravit. 22 Cum primus quoque aera signaret, servavit et in hoc p53Saturni reverentiam, ut, quoniam ille navi fuerat advectus, ex una quidem parte sui capitis effigies, ex altera vero navis exprimeretur, quo Saturni memoriam in posteros propagaret. Aes ita fuisse signatum hodieque intellegitur in aleae lusum, cum pueri denarios in sublime iactantes capita aut navia lusu teste vetustatis exclamant.
Apparently there was a Roman tradition connecting the Ianiculus with Ianus.
The Alphons X "Grande e General Storia" (ca. 1270) captures the legend. Now, Janus is a Noah's son, and Saturn his successor (book 3, chapters 21-22). It cites Esiodoro's "History of Roma's wonders" as source...but I don't know who is this Esiodoro. A. Millares Carló "Literatura Española hasta el siglo XV" (Madrid, 1950, p. 150), says that "History of Roma's wonders", is, in reality, one of several "Mirabilia Romae", the anonymous guides of the city made in 12th century.
Thanks, Fermin. I have passed your response on to my friend Keith. Do not know either work, but am wondering if Esiodoro may not be Spanish rendition of the Greek Hesiod, with his name attached to a perhaps Spanish redaction of one the "Mirablia Romae" you mention, to add authority to the work.
Dear Kathleen, I agree. More on this issue: Solalinde, Antonio G.. "Fuentes de la "General Estoria" de Alfonso el Sabio. III. Mirabilia Romae" Revista de filología española, 23 (1936) p. 113-142. The author says that the attribution to Hesiod is an erroneous reading of one sentence "ut Escodius (sic) scripsit"