Proclus Hymn #5

Χαῖρε, Θεῶν μῆτερ, πολυώνυμε, καλλιγένεθλε.
Χαῖρ’, Ἑκάτη προθύραιε, μεγασθενές. Ἀλλὰ καὶ αὐτὸς
Χαῖρ’, Ἴανε προπάτορ, Ζεῦ ἄφθιτε, χαῖρ’, ὕπατε Ζεῦ.

Τεύχετε δ’ αἰγλήεσσαν ἐμοῦ βιότοιο πορείην
βριθομένην ἀγαθοῖσι, κακὰς δ’ ἀπελαύνετε νούσους
ἐκ ῥεθέων, ψυχὴν δὲ περὶ χθονὶ μαργαίνουσαν
ἕλκετ’ ἐγερσινόοισι καθηραμένην τελετῇσι.
Ναί, λίτομαι, δότε χεῖρα, θεοφραδέας τε κελεύθους
δείξατέ μοι χατέοντι. Φάος δ’ ἐρίτιμον ἀθρήσω,
κυανέης ὥθεν ἔστι φυγεῖν κακότητα γενέθλης.
Ναί, λίτομαι, δότε χεῖρα, καὶ ὑμετέροισιν ἀήταις
ὅρμον ἐς εὐσεβίης με πελάσσατε κεκμηῶτα.

Χαῖρε, Θεῶν μῆτερ, πολυώνυμε, καλλιγένεθλε.
Χαῖρ’, Ἑκάτη προθύραιε, μεγασθενές. Ἀλλὰ καὶ αὐτὸς
Χαῖρ’, Ἴανε προπάτορ, Ζεῦ ἄφθιτε, χαῖρ’, ὕπατε Ζεῦ.

"Hail Mother of the Gods, who has many names, blessed with wonderful children.
Hail Hekate Prothyraia, of great strength. But You too,
hail forefather Janus, Zeus imperishable; hail supreme Zeus.
Make the course of my life radiant,
weighed down with good things, but drive the evil diseases
from my limbs; attract my soul, now madly raving around the earth,
once it has been purified through the intellect-awakening rites.
Yes, I beg You, give Your hand and show me, as to one in need,
the paths revealed by the Gods. I will observe the precious light,
from which comes the possibility to flee the misery of dark birth.
Yes, I beg You, give me Your hand, and with Your winds take me
to the harbor of piety, exhausted as I am.
Hail Mother of the Gods, who has many names, blessed with wonderful children.
Hail Hekate Prothyraia, of great strength. But You too,
hail forefather Janus, Zeus imperishable; hail supreme Zeus."

Hymn to the Mother of the Gods, to Hecate, to Janus
Proklos

So if I read this correctly, the Roman deity Ianus was syncretised with Zeus by the Hellenes?

By the Roman era yes, Ianus had come to be seen as a form of Iovis/Ζεύς, at least by the sensibilities of Proclus, who wrote from a heavily Orphic late-Platonism, which was certainly more energetically universalistic than some other Late Antique religions.

In any case, I think it's a clear and solid application of interpretatio.

You're not familiar with the Hymns of Proclus, J_Agathokles? I'm surprised

Jk, sort of

Oh I heard of them, and have Dutch translations of them, as well as Thoma Taylor's English ones. But I'm not particularly well-read on Proclus and his philosophies.