Modern street view of the Church

 

Engraving of the Church
Giovanni Battista Falda (1665)

The Temple is traditionally held to have been dedicated by Emperor Maxentius to his son and co-consul Valerius Romulus, who died in 309 and was given divine honours. The temple building was probably part of a rebuilding program of "incredible intensity" undertaken by Maxentius in the area, following a disastrous fire in 306; the project was only part-complete at his death. The temple's identification with Valerius Romulus is tentative, based on the spot-find of a coin dated to 307 AD showing the distinctive shape of the building, and a nearby dedication to Valerius Romulus as a divinised mortal.[1] The temple has also been speculated as a rebuilding of the original temple of "Jupiter Stator", or one dedicated to Penates, restored by Maxentius.

The 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 Arabian Christian 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. The apse was decorated with a Roman-Byzantine mosaic, representing a parousia, the Second Coming of Christ at the end of time. The bodies of Saints Mark and Marcellian were translated, perhaps in the ninth century, to this church, where they were rediscovered in 1583 during the reign of Pope Gregory XIII.

In 1632, Pope Urban VIII ordered the restoration of the basilica. The works, projected by Orazio Torriani and directed by Luigi Arrigucci, raised the floor level seven metres, bringing it equal with the Campo Vaccino, thus avoiding the infiltration of water. Also, a cloister was added. The old floor of the basilica is still visible in the lower church, which is actually the lower part of the first church.

In 1947, the restorations of the Imperial Forums gave a new structure to the church. The old entrance, through the Temple of Romulus, was closed, and the temple restored to its original forms; with the Pantheon, the Temple of Romulus is the best preserved pagan temple in Rome. A new entrance was opened on the opposite side (on via dei Fori Imperiali), whose arch gives access to the cloister, and through this to the side of the basilica.