Temple of Valerius Romulus and the northern aisle of the Basilica of Maxentius, Rome. View from the northern Palatine Hill.

Temple of Romulus (left) and Remains of the Basilica of Maxentius and Constantine at center, medieval church Santa Francesca Romana to right. View from the northern Palatine Hill.

In ancient Rome a basilica was a rectangular building with a large central open space, and often a raised apse at the far end from the entrance. Basilicas served a variety of functions, including a combination of a court-house, council chamber and meeting hall. There might be, however, numerous statues of the gods displayed in niches set into the walls. Under Constantine and his successors this type of building was chosen as the basis for the design of the larger places of Christian worship, presumably as the basilica form had fewer pagan associations than those of the designs of traditional Greco-Roman temples, and allowed large congregations. As a result of the building programmes of the Christian Roman emperors the term basilica later became largely synonymous with a large church or cathedral.

The Basilica of Maxentius and Constantine (sometimes known as the Basilica Nova - meaning "new basilica" - or Basilica of Maxentius) is an ancient building in the Roman Forum, Rome, Italy. It was the largest building in the Forum. The building's northern aisle is all that remains today.
Construction began on the northern side of the forum under the emperor Maxentius in 308, and was completed in 312 by Constantine I after his defeat of Maxentius at the Battle of the Milvian Bridge. The building rose close to the Temple of Peace, at that time probably neglected, and the Temple of Venus and Rome, whose reconstruction was part of Maxentius' interventions.
The building consisted of a central nave covered by three groin vaults suspended 39 meters above the floor on four large piers, ending in an apse at the western end containing a colossal statue of Constantine (remnants of which are now in a courtyard of the Palazzo dei Conservatori of the Musei Capitolini). The south and central sections were probably destroyed by the earthquake of 847. In 1349 the vault of the nave collapsed in another earthquake. The only one of the eight 20-meter-high columns, which survived the earthquake was brought by Pope Paul V to Piazza Santa Maria Maggiore in 1614. All that remains of the basilica today is the north aisle with its three concrete barrel vaults.

The Temple of Romulus was dedicated by Emperor Maxentius to his son Valerius Romulus, who died in childhood in 309 and was rendered divine honours. A coin from 307 AD depicting the unusual round shape of the building, associates this building with Maxentius. It is possible that the temple was originally the temple of "Jupiter Stator" or the one dedicated to Penates, and that Maxentius restored it before the re-dedication.
The ancient Roman temple was Christianized and dedicated to Sancti Cosma et Damianus in 527, when Theodoric the Great, king of the Ostrogoths, and his daughter Amalasuntha donated the library of the Forum of Peace (Bibliotheca Pacis) and a portion of the Temple of Romulus to Pope Felix IV. The pope united the two buildings to create a basilica devoted to two Greek brothers and saints, Cosmas and Damian, in contrast with the ancient pagan cult of the two brothers Castor and Pollux, who had been worshipped in the nearby Temple of Castor and Pollux.

Santa Francesca Romana, previously known as Santa Maria Nova, is a church in Rome, Italy, situated next to the Roman Forum in the rione Campitelli. The church was built in the second half of the tenth century, incorporating an eighth-century oratory that Pope Paul I excavated in the wing of the portico of the Temple of Venus and Roma.

more on https://en.wikipedia.org/wiki/Santi_Cosma_e_Damiano , https://en.wikipedia.org/wiki/Basilica_of_Maxentius and https://en.wikipedia.org/wiki/Santa_Francesca_Romana,_Rome