Dionysius of Halicarnassus relates a legend of the apparition of the Dioscuri, Castor and Pollux, to Postumius, in the attic on the army of the Latins. They appeared on horseback, and

"charged at the head of the Roman horse, wounding with their spears all they encountered, and driving the Latins before them. After the battle was over, they appeared in the Roman Forum, at the beginning of night... they then dismounted, and washed themselves in the stream, which rises near to the Temple of Vesta^l Of this extraordinary and wonderful apparition there are many memorials in Rome, as the Temple of Castor and Pollux, which the Roman people erected in the Forum where they appeared, and the stream near it, said to be dedicated to them," &c. [The fountain, of which there are remains, was built on this spot.]

This temple was rebuilt by Tiberius,^m and the columns are of his time; but although the temple was rebuilt from the foundations, the foundations themselves were not rebuilt, and the solid basement or podium of it is of the time of the Kings, of the second period, built of the large blocks of tufa, each of a ton weight, which made as good a foundation as any architect could require.ⁿ

The first distinct notice we have of a Temple of Castor in Rome is in the year 256 (B.C. 487), when the Dictator Postumius, in the war with the Latins and family of the Tarquins, vowed to build one.^o This vow was fulfilled by his son, and the temple was dedicated in the year of Rome 274 (B.C. 479), but no exact site is mentioned for this.^p The next notice of it is, that a bronze plate was fixed there in A.U.C. 415 (B.C. 337), to commemorate the conquest of the Latins.^q The next and the last notice of it in Livy, is that an equestrian statue of Marcius was ordered to be placed in the Forum, in front of the Temple of Castor,^r to commemorate his triumph over the Hernicians. This is also mentioned by Cicero^s as a statue in the Forum before Castor. Aurelius Victor mentions the Temple of Castor at the lake of Juturna, which agrees with this site. This temple was rebuilt by Augustus, and dedicated by Tiberius,^t in A.U.C. 759, A.D. 6, on the 27th of January, as mentioned by Ovid,^u who also mentions it as near the lake of Juturna.^v

In the Regionary Catalogue the dedication is given as to Castor and Minerva, Templum Castoris et Minervae. This is a singular deviation from the usual account of the dedication of the temple to Castor and Pollux, for which it is not easy to account, but it can hardly mean two temples.

The Temple of Castor and Pollux being thus ascertained, we are thereby enabled to fix another point hitherto doubtful. Suetonius mentions that Caligula used this temple as a vestibule to his place. The great brick building of the time of Caligula which stands close to it, on the same level, and is only separated from it by the pavement of the street, must therefore be the Palace of Caligula, which has hitherto been placed on the Palatine Hill, fifty feet above it...

l. This description agrees with the site of this ruin. The Temple of Vesta was in front of the church of S. Maria Liberatrice, close to this spot.

m. Dion. Cass. Hist., lib. lv. c. 27.

n. See No. 3157.

o. Livii Hist., lib. ii. c. 20.

p. Livii Hist., lib. ii. c. 42

q. Ibid., lib. viii. c. 11.

r. Ibid., lib. ix. c. 43.

s. Cicero Philipp., vi. c.5.

t. Suetonius in Tiberio, c. 20; Dion. Cassius, lib. lv. c. 27.

u. "Fratribus illa deis fratres de gente deorum Circa Juturnae composuere lacus."

v. The English word lake does not convey the true meaning of the Latin word lacus, which certainly means sometimes the loch of a canal, and probably also the basin of a fountain.

John Henry Parker, The archaeology of Rome (London: John Murray, 1876), 22-23.