The temple of Castor and Pollux probably dates as far back as the year 487 before Christ, when the dictator Postumius vowed to build a monument in commemoration of his victory at the great battle of Lake Regillus, with which the mythical history of Rome closes.  It recalls the well-known romantic legend of the mysterious interference of the Dioscuri in that memorable struggle which Macaulay has woven into one of the most spirited of his Lays.  The temple is supposed to have been erected on the spot where the divine Twins announced the victory to the people in the Forum at the close of the day.  About twenty feet from the eastern corner of the temple are slight remains of a shallow oval basin, which has been identified as the lake or fountain of Juturna, the wife of Janus, the Sabine war-god, where the Dioscuri washed their armour and horses from the blood and dust of the fray.  It was probably at first a natural spring gushing out of the tufa rock of the Palatine Hill, but being dried up, it became in later times a lacus or basin artificially supplied with water.  For long ages afterwards the anniversary of the great battle was celebrated every year on the fifteenth of July by a splendid pageant worthy of the greatness of the empire.  The Roman knights, clothed in purple robes, and crowned with olive wreaths, and bearing their trophies, first offered sacrifice in the shrine of Castor and Pollux, and then formed a procession, in which five thousand persons sometimes took part, which filed in front of the temple and marched through the city.

The original building having stood for nearly five hundred years, it began to exhibit signs of decay, and accordingly it was rebuilt upon the old foundations by Augustus, and dedicated by Tiberius.  The podium or mass of rubble masonry therefore which we see beneath the three columns at the present day belongs to the time of the kings, while the columns themselves belong to the imperial period.  Caligula used the temple as a vestibule to his palace on the Palatine Hill immediately behind.  On the brow of that hill, separated only by the pavement of the modern street, projects a labyrinth of vaults, arches, and broken walls, a mighty maze of desolation without a plan, so interspersed with verdure and foliage that “it looks as much a landscape as a ruin.”  This is supposed to be the palace of Caligula; and its remains abundantly attest the extraordinary magnificence of this imperial domain, which contained all that was rich and rare from the golden East, from beyond the snowy Alps, and from Greece, the home of art.  The substructions of this mighty ruin are truly astonishing; they are so vast, so massive, so enduring, that they seem as if built by giants.  Concealed by modern houses built up against the foot of the palace, some of the remains of the famous bridge which Caligula threw obliquely over the Forum can be made out; two of the tall brick piers are visible above the houses, and in the gable of the outer house the spring of one