"Let us call to witness the priests of Cyprus who set up common altars to Helios and Zeus; but even before them let us summon as witness Apollo, who sits in council with our God. For this God declares: "Zeus, Hades, Helios Serapis, three Gods in one godhead!" Let us then assume that, among the intellectual Gods, Helios and Zeus have a joint or rather a single sovereignty. Hence I think that with reason Plato called Hades a wise God. And we call this same God Hades Serapis also, namely the Unseen and Intellectual, to whom Plato says the souls of those who have lived most righteously and justly mount upwards."
From the Hymn to King Helios, Emperor Julian

(Jasper Intaglio Ring Stone of Serapis; private collection)