As the elder Caesar had made a vow at Pharsalia, so the younger Caasar made a vow at Philippi. The vow was to Mars Ultor, and was duly fulfilled. The house of Mars the Avenger likewise became the centre of a new Forum. This temple, dedicated by its founder on the first of his own month in 2 B.C., served as the resting-place of the standards which his diplomacy had recovered from the Parthians. The Forum Augustum adjoined that of Caesar on the north-east side. It was rectangular in shape, but on the east and west sides there were semi-circular spaces with porticoes in which statues of Roman generals in triumphal robes were set up. It became the practice that in this Forum, the members of the imperial family should assume the toga virilis; and when victorious generals were honored by statues of bronze, they were set up here. These fora of the first Caesars, father and son, were the beginning of a rehabilitation of this quarter of the city, which was resumed, a century later, by the Emperors Nerva and Trajan; and they established an easy communication between the Forum and the Field of Mars. Hitherto the way from the Campus to the Forum had been round by the west and south sides of the Capitoline, through the Porta Carmentalis.
The Campus Martius itself, whether taken in the wider or the narrower sense, put on a new aspect under the auspices of the Caesars. The Campus in the stricter sense was bounded on the south by the Circus Flaminius and on the east by the Via Lata. It was the great rival of Caesar who set the example of building on this ground. In 55 B.C. Pompey erected his “Marble Theatre”. Caesar began the construction of marble Saepta—an enclosure for the voting of the centuries—which was finished by Agrippa. The name of Agrippa has more claim to be associated with the Field of Mars than either Caesar’s or Pompey’s. The construction of the Pantheon, which is preserved to the present day, was due to his enterprise. This edifice is of circular form and crowned with a dome, which was originally covered with tiles of gilt bronze. The dome is an instance “of the extraordinarily skillful use of concrete by the Romans; it is cast in one solid mass, and is as free from lateral thrust as if it were cut out of one block of stone. Though having the arch form, it is in no way constructed on the principle of the arch”. The building is lighted only from the top. “The interior measures 132 feet in diameter, as well as in height. The walls are broken by seven niches, three semicircular, and, alternating with them, three rectangular, wherein, at a later period, splendid marble columns with entablatures were introduced. Above this rises an attica with pilasters, the original portion of which has undoubtedly been changed, since we know that Diogenes Caryatides once rose above the entablatures of the columns, and divided the apertures of the great niches. Above the attica rises, in the form of a hemisphere, the enormous dome, which has an opening in the top twenty-six feet in diameter, through which a flood of light pours into the space beneath. Its simple regularity, the beauty of its parts, the magnificence of the materials employed, the quiet harmony resulting from the method of illumination, give to the interior a solemnly sublime character, which has hardly been impaired, even by the subsequent somewhat inharmonious alterations. These have especially affected the dome, the beautiful and effectively graded panels of which were formerly richly adorned with bronze ornaments. Only the splendid columns of yellow marble (giallo antico), with white marble capitals and bases, and the marble decorations of the lower walls, bear witness to the earlier magnificence of the building. The porch is adorned with sixteen Corinthian columns”.
Agrippa also built the adjacent baths called after him, Thermae Agrippae (27 and 25 B.C.), and a basilica, which he dedicated to Neptune in memory of his naval victories, and enclosed with a portico which from the pictures adorning it was called the Portico of the Argonauts. Another wealthy noble of the day, Statilius Taurus, constructed the first stone amphitheatre in Rome, and its site, too, was somewhere in the Field of Mars. The first Princeps himself seemed content to leave the adornment of the Campus chiefly to the munificence of his lesser fellow-citizens. But much further north than all the buildings which have been mentioned, where the Campus becomes narrow by the approach of the Via Flaminia to the river, he built a great mausoleum for the Julian family, a round structure surmounted by a statue of himself.
On the south side of the Flaminian Circus, in the Prata Flaminia, a region which might be included in the Campus, in a wider sense of the name, Augustus erected the Porticus Octaviae in the name of his sister, and attached to it a library and a collection of works of art. It was close to the Templum Herculis Musarum built by Fulvius Nobilior, the patron of the poet Ennius, and renewed under Augustus, and surrounded by a portico which was dedicated as the Porticus Philippi, in honor of L. Marcius Philippus, the step-father of the Emperor. Near the Portico of Octavia, were the Theatres of Balbus and Marcellus, both dedicated in the same year (11 B.C.). The first was one of those works which the rich men of the day executed through the influence and example of Augustus. The second had been begun by Caesar, but was finished by Augustus and dedicated in the name of his nephew Marcellus. The Porticus Octavii (close to the Flaminian Circus), which was dedicated by Cn. Octavius after the victory over Perseus, was burnt down and restored under Augustus. It was remarkable as the earliest example of Corinthian pillars at Rome.
From the Forum the Clivus Capitolinus, passing the temple of Saturn, led up to the saddle of the Mons Capitolinus, the smallest of all the mountains of Rome. Thence it ascended to the southern height, called specially the Capitolium, the citadel of Servian Rome, where the treaties with foreign nations were kept and triumphal spoils were dedicated. Another path led up to the northern height, the Arx, which underwent, little change under the Empire. But on the southern hill it was otherwise; there new buildings arose under the auspices of Augustus. The highest part of the hill was occupied by the great temple of Jupiter Optimus Maximus, in which the senate used to meet on certain solemn occasions. This temple, burnt down in 83 B.C. had been rebuilt, but it required and received costly repairs in the time of Augustus. Ranged around it on lower ground were many lesser temples, of which that of Jupiter Feretrius, to whom Romulus dedicated his spolia opima, and that of Fides founded by Numa, may he specially mentioned. Augustus increased their number. In 20 B.C. he dedicated the round temple of Mars Ultor, and in 22 B.C. that of Jupiter Tonans, in memory of an occasion, during his Cantabrian expedition, on which he had narrowly escaped death by lightning. This temple, marvelous for its splendor, attracted multitudes of visitors and worshippers, and its position at the point where the Clivus reached the Area Capitolina might suggest that Jupiter Tonans was a sort of gatekeeper for the greater Jupiter on the summit.
But the Palatine Mount was the centre from which the development of Rome went out. It was the original Rome, the Roma quadrata, where were localized the legends of its foundation. There were to be seen the Casa Romuli, the Lupercal where Romulus and Remus were fed by the wolf, the cornel-tree, and the mundus, receptacle of those things which at the foundation of the city were buried to ensure its prosperity. Under the Republic, the Palatine was the quarter where the great nobles and public men lived. Augustus himself was born there, and there he built his house. So it came about that the name which designated the city of Rome in its earliest shape, Palatium, became the name of the private residence of its first citizen. The palace of Augustus was a magnificent building in the new and costly style which had only recently been introduced in Rome. Ovid, standing in imagination by the temple of Jupiter Stator, where the Palatine hill slopes down to the Via Sacra, could see the splendid front of the palace, “worthy of a god”.
Singula dum miror, video fulgentibus armis
Conspicuo postes tectaque digna deo.
The other great building by which Augustus transformed the appearance of the Palatine was the temple of Apollo, begun in 36 B.C. after the end of the war with Sextus Pompeius, and dedicated eight years later. It was an eight-pillared peripteros, built of the white marble of Luna, and richly adorned with works of art. The chief sight was the colossus of bronze representing Augustus himself under the form of Apollo. Between the columns stood the statues of the fifty Danaids, and over against them their wooers, the sons of Aegyptus, mourned on horseback. Under the statue of the god were deposited in a vault the Sibylline Books. In the porticoes were two libraries, one Latin and one Greek.
On the northern slope of the Palatine, facing the Capitol, stood the temple of Augustus, which Tiberius and the Empress Livia