Apparently no temple, in our sense of the word, was ever erected to Jupiter on this his holy mountain; as god of the sky and thunder he appropriately received the homage of his worshippers in the open air. The massive wall, of which some remains still enclose the old garden of the Passionist monastery, seems to have been part of the sacred precinct which Tarquin the Proud, the last king of Rome, marked out for the solemn annual assembly of the Latin League. The god's oldest sanctuary on this airy mountain-top was a grove; and bearing in mind not merely the special consecration of the oak to Jupiter, but also the traditional oak crown of the Alban kings and the analogy of the Capitoline Jupiter at Rome, we may suppose that the trees in the grove were oaks. We know that in antiquity Mount Algidus, an outlying group of the Alban hills, was covered with dark forests of oak; and among the tribes who belonged to the Latin League in the earliest days, and were entitled to share the flesh of the white bull sacrificed on the Alban Mount, there was one whose members styled themselves the Men of the Oak, doubtless on account of the woods among which they dwelt.
But we should err if we pictured to ourselves the country as covered in historical times with an unbroken forest of oaks. Theophrastus has left us a description of the woods of Latium as they were in the fourth century before Christ. He says: The land of the Latins is all moist. The plains produce laurels, myrtles, and wonderful beeches; for they fell trees of such a size that a single stem suffices for the keel of a Tyrrhenian ship. Pines and firs grow in the mountains. What they call the land of Circe is a lofty headland thickly wooded with oak, myrtle, and luxuriant laurels. The natives say that Circe dwelt there, and they show the grave of Elpenor, from which grow myrtles such as wreaths are made of, whereas the other myrtle-trees are tall. Thus the prospect from the top of the Alban Mount in the early days of Rome must have been very different in some respects from what it is to-day. The purple Apennines, indeed, in their eternal calm on the one hand, and the shining Mediterranean in its eternal unrest on the other, no doubt looked then much as they look now, whether bathed in sunshine, or chequered by the fleeting shadows of clouds; but instead of the desolate brown expanse of the fever-stricken Campagna, spanned by its long lines of ruined aqueducts, like the broken arches of the bridge in the vision of Mirza, the eye must have ranged over woodlands that stretched away, mile after mile, on all sides, till their varied hues of green or autumnal scarlet and gold melted insensibly into the blue of the distant mountains and sea.
But Jupiter did not reign alone on the top of his holy mountain. He had his consort with him, the goddess Juno, who was worshipped here under the same title, Moneta, as on the Capitol at Rome. As the oak crown was sacred to Jupiter and Juno on the Capitol, so we may suppose it was on the Alban Mount, from which the Capitoline worship was derived. Thus the oak-god would have his oak-goddess in the sacred oak grove. So at Dodona the oak-god Zeus was coupled with Dione, whose very name is only a dialectically different form of Juno; and so on the top of Mount Cithaeron, as we have seen, he appears to have been periodically wedded to an oaken image of Hera. It is probable, though it cannot be positively proved, that the sacred marriage of Jupiter and Juno was annually celebrated by all the peoples of the Latin stock in the month which they named after the goddess, the midsummer month of June.
If at any time of the year the Romans celebrated the sacred marriage of Jupiter and Juno, as the Greeks commonly celebrated the corresponding marriage of Zeus and Hera, we may suppose that under the Republic the ceremony was either performed over images of the divine pair or acted by the Flamen Dialis and his wife the Flaminica. For the Flamen Dialis was the priest of Jove; indeed, ancient and modern writers have regarded him, with much probability, as a living image of Jupiter, a human embodiment of the sky-god. In earlier times the Roman king, as representative of Jupiter, would naturally play the part of the heavenly bridegroom at the sacred marriage, while his queen would figure as the heavenly bride, just as in Egypt the king and queen masqueraded in the character of deities, and as at Athens the queen annually wedded the vine-god Dionysus. That the Roman king and queen should act the parts of Jupiter and Juno would seem all the more natural because these deities themselves bore the title of King and Queen.
Whether that was so or not, the legend of Numa and Egeria appears to embody a reminiscence of a time when the priestly king himself played the part of the divine bridegroom; and as we have seen reason to suppose that the Roman kings personated the oak-god, while Egeria is expressly said to have been an oak-nymph, the story of their union in the sacred grove raises a presumption that at Rome in the regal period a ceremony was periodically performed exactly analogous to that which was annually celebrated at Athens down to the time of Aristotle. The marriage of the King of Rome to the oak-goddess, like the wedding of the vine-god to the Queen of Athens, must have been intended to quicken the growth of vegetation by homoeopathic magic. Of the two forms of the rite we can hardly doubt that the Roman was the older, and that long before the northern invaders met with the vine on the shores of the Mediterranean their forefathers had married the tree-god to the tree-goddess in the vast oak forests of Central and Northern Europe. In the England of our day the forests have mostly disappeared, yet still on many a village green and in many a country lane a faded image of the sacred marriage lingers in the rustic pageantry of May Day.