Three immense vaults of the Basilica of Constantine or Maxentius dominate the Forum's northeastern end. Little is known of the early days of this building; it came too late into the ancient world to find a place among the great descriptions in Latin literature, though it is mentioned briefly in several writings of the fourth and fifth centuries, including the Notitia or Regionary Catalogue. Maxentius began it during his brief period of power from A.D. 306 to 312, on a site which excavation has shown to have been occupied at various times by private houses, part of the portico of Nero's Golden House, and markets and storehouses.
As first planned, it had a nave and two aisles running lengthwise approximately east and west, parallel to the Roman Forum and opening eastward through an arched portico toward the Colosseum. At the west end of the nave, opposite this entrance, was a large apse where, in the fifteenth century, were found parts of a colossal statue of Constantine, now in the Conservatori Museum.
Constantine changed this plan by adding another entrance at the south side so that the building opened on the Forum as well as toward the Colosseum. He also built another apse opposite this entrance, in the central compartment of the north aisle, which, like its southern counterpart, was divided into three barrel-vaulted sections, each large enough to contain a good-sized building.
It is this north aisle, with Constantine's apse, which towers impressively beyond the Forum today. Part of the western end wall, with the apse of Maxentius, also stands, and here and there jagged fragments of masonry which belonged to the great piers of the nave still rise from the high platform on which the basilica rests.
The building was of brick-faced concrete, the interior walls panelled with marble, the brick coffering of its vaults covered with stucco. Fluted marble columns with richly carved Corinthian capitals originally stood against the piers, apparently carrying the weight of the massive crossvaulting of the nave, though this was actually borne by the piers themselves. The last of these marble columns, one of which still appears in place in prints and drawings of the sixteenth century, was taken away in the seventeenth and set up in the Piazza of Santa Maria Maggiore to bear the statue of the Virgin.
Just when the nave and south aisle collapsed is unknown. Probably they were badly damaged by the earthquake of the ninth century and perhaps by a later one as well. By the Middle Ages the mass of ruin was a giant quarry for building materials; as it began to emerge from the realm of legend into that of record, the remnant was in use for such purposes as hay lofts, cattle sheds, drill grounds, and a riding school.
The building was far too large to be converted easily into a church; its central nave was over 262 feet long, more than 97 feet wide, and almost 115 feet high. It would have required the genius and technical resources of a Michelangelo to make use of it, as he later did the central hall of the Baths of Diocletian, but by his time the basilica was in the same state of ruin as today. The barrel vaulting of its aisle, however, was one of Bramante's inspirations for the plan he proposed for the new Saint Peter's.
The great ruin has gone by various names throughout its long history. Most early records call it simply the New Basilica, but by the sixth century its true identity was so far forgotten that it was referred to as the 'Temple of Rome' and later as the 'Temple of Romulus'. By the fifteenth century it was known as the 'Temple of Peace,' from the actual but longsince-vanished temple which stood nearby in Vespasian's forum of that name. With the name went the associations of the real Temple of Peace. The basilica was believed to have been built by Vespasian and to have housed the plunder of the temple at Jerusalem and innumerable other treasures. It was called 'the Temple of Peace' well into the nineteenth century. In Rome today it is better known by the name of Maxentius, who began it, than by that of Constantine, who completed it.
John Evelyn Diary for 1644 gives a typical gentleman's glimpse of the ruin as it was known in the seventeenth century:
'We went into the Campo Vaccino, by the ruins of the Temple of Peace, built by Titus Vespasianus, and thought to be the largest as well as the most richly furnished of all the Roman dedicated places: it is now a heap rather than a temple, yet the roof and volto continue firm, showing it to have been formerly of incomparable workmanship.' Evelyn adds the surprising statement, contradicted by his own dating of it in Vespasian's time: 'This goodly structure was, none know how, consumed by fire the very night, by all computation, that our Blessed Saviour was born.'
Almost two centuries later the American traveller, Theodore Dwight, described the ruin as it appeared to the romantic visitor:
'Nearly opposite to us on the other side of the Forum were the remains of the Temple of Peace, which are supposed to have formed for the time the vestibule of Nero's house; and here we were struck with astonishment, having never seen such wide and noble arches. . . . The remaining arches of the Temple of Peace have been left exposed to the sunshine and rain, hallowed however in the eyes of the people by a small cross elevated at the top, among the shrubbery with which it is crowned, to preserve them from dilapidation, though cattle often wander to its shade from the Forum (which in Italian bears the name of Cow-Pasture), and lie quietly down in the inmost recesses of the temple.'
The basilica's great vaults have been put to a new use since 1933; a use which would undoubtedly have pleased the dwellers in ancient Rome as much as it does her citizens and visitors today. On spring afternoons and summer nights, concerts by orchestra and chorus are held in its great area, the musicians stationed beneath an inconspicuous shell built into Constantine's apse. Besides the crowds which can be seated on chairs and benches, adventurous climbers find superior accommodations on the tops of the ruined piers, and black-frocked priests listen from the roof of the neighbouring church of Saints Cosmas and Damian. The vaults are lit by night with an orange glow, which throws their deep coffering into strong relief. Beyond the arches of the portico the Colosseum gleams in silver floodlight, while the façade of Santa Francesca Romana and sometimes the buildings in the Forum as well stand out red or green or orange against the blue-black sky.