NEPTUNALIA, a festival of Neptune, celebrated at Rome, of which very little is known (Varro, de Ling. Lat. VI.19). The day on which it was held, was probably the 23d of July. In the ancient calendaria this days is marked as Nept. ludi et feriæ, or Nept. ludi, from which we see that the festival was celebrated with games. Respecting the ceremonies of this festival nothing is known, except that the people used to build huts of branches and foliage, in which they probably feasted, drank, and amused themselves (Horat. Carm. III.28.1, &c.; Tertull. De Spect. 6).
—Leonhard Schmitz, in William Smith's Dictionary of Greek and Roman Antiquities (John Murray, London, 1875).
Horace, Odes, III.28, my translation
Hearty Lydë, for Neptune’s day,
What’s more fitting than this? Pour out our hidden store;
Go, unbarrel the Cæcuban,
And drive reason away; ruin its mighty seat.
Now you see that the noonday sun
Bends to the west, yet you would spare the wine
Which was barrelled ere forty years?
Thinkst that flittering time stands for a single hour?
I will sing of the Ocean’s god,
You, of the briny braids wrapped on the Nerieds.
Then you’ll play with a bending lyre
Songs of Leto the old; songs of her daughter’s shafts.
Next the goddess of Cnidon’s shrine
Earns the height of our songs, guard of the shining isles,
where she rides in a train of swans;
Last we’ll mourn for the Night, uttering quiet songs.
Neptuni faciam? Prome reconditum,
Lyde, strenua Cæcubum
Munitæque adhibe vim sapientiæ.
Sentis? ac veluti stet volucris dies,
Parcis deripere horreo
Cessantem Bibuli consulis amphoram.
Nos cantabimus invicem
Neptunum et viridis Nereïdum choros,
Tu curva recines lyra
Latonam et celeris spicula Cynthiæ;
Summo carmine, quae Cnidon
Fulgentisque tenet Cycladas et Paphum
Junctis visit oloribus;
Dicetur merita Nox quoque nenia.