The church of saints Cosmas and Damian was founded by Pope Felix IV (526-530), who adapted to the Christian worship two classic buildings, which were received as a gift from the daughter of Theodoric, Amalasunta: the Library of Forum Pacis, (1st Century A.D.), and a Maxentian dome commonly known as the Temple of the Divine Romulus, but now rather identified as the Temple of the household gods.
With the church of saint Maria Antiqua, the church of saints Cosmas and Damian was the first place of Christian worship in the area of the Forum; since it had no parish function, it became a true and proper sanctuary where the faithful had gone to pray for healing to two holy miracle-workers, Cosmas and Damian, who were martyred military doctors. Under Serge I (695) the church was enriched with an ambo, a tabernacle and the decoration of the arch of the apse; at the time of Hadrian I (772), it became a cardinal-deacon and collegiate church and estates were assigned to provide for its functions.
During the Middle Ages, the church did not suffer big transformations; probably already at the time of Felix IV, its ambiance appeared as a hall with an apse, thus requiring minimal intervention to be converted into a sacred building. In the XII century, a transverse wall, supported by columns, was built between the third and the fourth window; probably to ensure the stability of the building. For the rest, the interior of the sanctuary remained essentially unchanged until the end of XVI century. In 1512 the church was assigned to the Third Order Regular of St. Francis, who still administers it. Between 1597 and 1602 there was the first significant intervention on the building, made necessary by the collapse of parts of the pillars, which led however to the irretrievable loss of the parts of the mosaics of the arch of the apse.
Between 1626 and 1632 there was a more radical makeover. It was decided to raise the level of the church of about seven meters because of the silting of the Forum, caused by frequent floods while leaving practically the lower part. Eventually, the floors of the lower church and the dome were also raised 90 cm. whose ancient bronze door was raised and moved to the left.
The raising of the floor surface inevitably changed the spatiality of the church, likewise the vision of the mosaics of the apse, which undergone further mortification with the inclusion of the main altar. Architected by Domenico Castelli (1637-38), reusing for canopy the marble columns of the old one, the new altar obscured much the mosaic decoration and the choir, that it became necessary to install a lantern at the top of the canopy of the apse. In turn, this operation resulted in the loss of the part of the decoration depicting the hand of the Lord who gives the crown to Christ. Finally, probably at the time of Clement IX (1667-69), a supporting arch was added as reinforcement to the arch of the apse, which ended to cover the mosaic decoration. In 1897, following the excavations of the Forum, the bronze door of the dome was returned to its original position, while in 1947 the current prospect of the basilica on the street in Miranda was erected.
The church of saints Cosmas and Damian houses many works of the Middle Ages. The first chapel to the right, based on the Crucifix, derives its name from the altarpiece: it is actually a fresco from the XIII century taken from the lower church, completely repainted in oil in the XVII century, remarkable for the iconography of Byzantine origin, which depicts Christ dressed in a long tunic. On the altar, it houses a Madonna with the Child, known as the Lady of Good Health or saint Gregory, dating from the end of the XII century and attributed to a Roman painter, who was not without Tuscan influences.
The painting represented originally the Virgin in full length, seated and with the Child, blessing, in her arms; however, the board had suffered the curtailment of the lower part, perhaps due to widespread loss of the color in the lower area. To the right of the altar is a candle stand for the Easter candle, a XVII century reworking of a cosmatesque work (XIII century). The basin of the arch contains the splendid mosaic at the time of Felix IV, depicting Christ coming down on Earth in the time of the second apocalyptic coming. Rested on a carpet of celestial clouds, Christ has to his sides saints Peter and Paul, who are presenting respectively saints Cosmas and Damian; to the left, Felix IV provides the model of the church, which he dedicated, while to the right, saint Theodore is depicted; below, in the fascia, twelve lambs are shown advancing towards the Divine Lamb, who is situated on a central mound.
This mosaic is a major work of art of the VI century, as it is still imbued of the courtly style of the late Roman imperial art.
Made with weave of exceptional quality, the mosaic has undergone several changes in time; Gregory XIII (1572-85), had replaced the head of Felix IV that of his namesake predecessor Gregory the Great; in 1669 Cardinal Francesco Barberini commissioned to Orazio Manenti a true and proper reconstruction of the left side of the mosaic, which also involved the restoration of the head of Felix IV. Other conservative interventions have taken place between the XIX and XX centuries; finally, the mosaic was again restored in 1988-89.
The mosaic decoration of the arch of the apse, unfortunately mutilated at the sides and under the arch, represents the first vision of the Apocalypse: to the center, the Lamb on the throne is depicted with the scroll of the seven seals, while the sides unfold the seven flaming candle stands and the four angels; unfortunately from among the four symbols of the evangelists Matthew (the angel on the right) and Giovanni (the eagle on the left) have only been preserved, as well as of the Twenty-Four Elders offering crowns, only six survived the XVII century transformation of the church.
In this mosaic the apocalyptic symbols are surrounded by a gold background, and have a very obvious character of symbolic abstraction. The beginnings of this mosaic dates back to the restoration campaign promoted by Pope Serge I in 695. The central part of the mosaic decoration underwent extensive reintegration in the restoration campaign of 1936-37.
In the sacristy, small ciborium of Cardinal Guido Pisani (cosmatesque work with mosaic decoration) is kept, the silver reliquary of saint Matthew (XI century) and an early medieval chalice. The lower church retains traces of the earliest phase of the church in the precosmatesque floor of the region of the apse perhaps from XVIII century, and in the marble altar dating to the VI-VII century. It is believed to be consecrated by saint Gregory the Great, but most likely it is in the time of Felix IV or Serge I.
In the wall below the dome (accessible from the precinct of the Roman Forum), some frescoes are preserved though much ruined. These could be traced back to Pope Urban IV (1261-1264). Attributed to a Roman artist, the frescoes are an intermediate stage between the large painting of Byzantine style and the new trends that were expressed at the end of the XII century with Cavallini and Torriti.
The frescoes represent: (a) the banquet in the house of the Pharisee, of which there remain only the part depicting Mary Magdalene washing the feet of the Redeemer, (b) the holy women at the tomb, (c) the Savior between Magdalene and Salome, and (d) the symbols of the Evangelists. There is also preserved an anonymous but extraordinary tomb perhaps intended to the titular cardinal Guido (died in 1149), which probably seemed modeled on the tomb of Alfano, the chamberlain to saint Maria in Cosmedin.