[152] The temple of the Palatine Apollo stood, according to Bianchini, a little beyond the triumphal arch of Titus. It appears, from the reverse of a medal of Augustus, to have been a rotondo, with an open portico, something like the temple of Vesta. The statues of the fifty daughters of Danae surrounded the portico; and opposite to them were their husbands on horseback. In this temple were preserved some of the finest works of the Greek artists, both in sculpture and painting. Here, in the presence of Augustus, Horace's Carmen Seculare was sung by twenty-seven noble youths and as many virgins. And here, as our author informs us, Augustus, towards the end of his reign, often assembled the senate. [153] The library adjoined the temple, and was under the protection of Apollo. Caius Julius Hegenus, a freedman of Augustus, and an eminent grammarian, was the librarian. [154] The three fluted Corinthian columns of white marble, which stand on the declivity of the Capitoline hill, are commonly supposed to be the remains of the temple of Jupiter Tonans, erected by Augustus. Part of the frieze and cornice are attached to them, which with the capitals of the columns are finely wrought. Suetonius tells us on what occasion this temple was erected. Of all the epithets given to Jupiter, none conveyed more terror to superstitious minds than that of the Thunderer-- Coelo tonantem credidimus Jovem Regnare.--Hor. 1. iii. Ode 5. We shall find this temple mentioned again in c. xci. of the life of Augustus. [155] The Portico of Octavia stood between the Flaminian circus and the theatre of Marcellus, enclosing the temples of Jupiter and Juno, said to have been built in the time of the republic. Several remains of them exist, in the Pescheria or fish-market; they were of the Corinthian order, and have been traced and engraved by Piranesi. [156] The magnificent theatre of Marcellus was built on the site where Suetonius has before informed us that Julius Caesar intended to erect one (p. 30). It stood between the portico of Octavia and the hill of the Capitol. Augustus gave it the name of his nephew Marcellus, though he was then dead. Its ruins are still to be seen in the Piazza Montanara, where the Orsini family have a palace erected on the site. [157] The theatre of Balbus was the third of the three permanent theatres of Rome. Those of Pompey and Marcellus have been already mentioned. [158] Among these were, at least, the noble portico, if not the whole, of the Pantheon, still the pride of Rome, under the name of the Rotondo, on the frieze of which may be seen the inscription, M. AGRIPPA. L. F. COS: TERTIUM. FECIT. Agrippa also built the temple of Neptune, and the portico of the Argonauts.