Santa Maria del Sole was the dedication of the small round 1st century BC temple in the Bocca della Verità neighbourhood, when it served as a devotional church. This is in the rione Ripa. Picture of the edifice on Wikimedia Commons here. There is an English Wikipedia article on the building as a temple, here.
The dedication was to the Blessed Virgin Mary, "of the sun".
The original temple dates to about 100 BC, and was originally dedicated to Hercules Victor (the traditional name of “Temple of Vesta” was an ignorant guess by Renaissance antiquarians). This dedication was confirmed by the discovery of part of the inscribed base of the cult statue it contained, which named the deity as Hercules Olivarius and the sculptor of the statue as Scopas Minor (a Greek).
The founder was a merchant called Marcus Octavius Herrenus, who probably dealt in olive oil since the deity was the patron of those who dealt in this commodity. He would have been able to make a fortune in the trade, since the oil was used for lamps as well as in food.
The temple was certainly of high status for its time. It was built of Greek marble and in a pure Greek style, with twenty Corinthian columns around a circular cella where the image of the deity was kept ( a temple such as this one which has a colonnaded portico on all sides is called peripteral). The large doorway faced east. This was the first marble building in Rome to have mostly survived. It was heavily restored in the reign of the emperor Tiberius, perhaps after a serious flood in AD 15.
Church of San Stefano
As the church of San Stefano Rotondo, it is first mentioned in a Papal bull of 1140 issued by Pope Innocent II. It must have been converted only a short time beforehand, and according to tradition this was done by the Savelli family. (The question remains unanswerable as to how the temple had survived until then.)
The possibility of the name causing confusion with the more famous San Stefano Rotondo al Celio is obvious, but the latter church was then known as San Stefano in Celio.
To effect the conversion, the roof and entablature were demolished and the material apparently used to wall up the spaces between the columns. The removal of the entablature was an odd thing to do structurally, but presumably the frieze bore a pagan dedicatory inscription which would have been offensive to Christians.
One column on the north side was also removed at some stage. This was possibly either to make way for an entrance to a proposed side chapel, or because some other church needed a column to make up a set (if so, it has never been traced).
The cella, however, was not demolished. So, the layout was a central circular space of rather cramped dimensions, surrounded by a circular passage formed by the blocking walls between the columns. This was a very odd arrangement, and looks as if it was intended as a pilgrimage shrine rather than as a church for a congregation. If so, something holy would have been kept in the cella, and pilgrims could then walk around it in the passage and presumably look at whatever it was through holes made in the cella walls.
Pope Sixtus IV (1471-84) arranged a restoration in 1475, which is commemorated by a surviving epigraph inside and has left a fresco.
In the 16th century the church was renamed San Stefano delle Carrozze (of the coachmen), and in the 17th century rededicated as Santa Maria del Sole.
Early illustrations, such as Piranesi's engraving of 1748, show a small campanile or bell-cote perched on the conical roof, with a round-headed space for one bell and a crowning pediment. The entrance had another triangular pediment over the molded doorcase, surmounted in turn by a dedicatory tablet, a large rectangular window and a coat-of-arms in stucco relief which reached the roofline.
Church of Santa Maria
The dedication to Santa Maria del Sole derives from a miraculous icon story which allegedly took place in 1560.
According to this, a very old lady called Geronima Latini had a brother who was rowing in a boat across the Tiber when he found a paper icon of Our Lady floating on the water. He rescued this, let it dry out and gave it to his sister who had taken private vows as a virgin. A few days later she had a vision in which the icon shone as brightly as the sun, and informed other people of this. As a result of popular devotion the icon was enshrined in this church.
The building was re-converted to an approximation of its original appearance during the French occupation by demolishing the blocking walls, substituting iron railings and removing the bell-cote. The entablature was not re-created, giving the building a degraded appearance which would have seriously offended the original builders. The building after this restoration is depicted in an engraving of 1817 by Luigi Rossini.
As a church it continued in use, until deconsecration between 1870 and 1890. The miraculous icon was then removed to the Oratorio del Santissimo Crocifisso, where it remains.
There was another gutting in 1935, which entailed the removal of any Christian fittings except some fresco fragments and an epigraph.
The structure was restored from 1988 to 1999, and provided with a new roof.
The original ribbed Corinthian columns were imported from Greece They are in Pentelic marble, and the capitals are Greek in style. Some of the latter have lost their upper halves.
The AD 15 restoration is evidenced from the fact that nine columns of the original twenty and eleven capitals are not of the original Greek marble, but are of Luna marble from Tuscany. The flood must have smashed the temple. The present structure has one column missing-look around the curve to the right of the entrance.
The columns stand on a stepped crepidoma on a foundation of Grotta Oscura tufo.
The cella within the columns has its lower courses in heavily restored white marble, and its upper portion in tufo with shallow blind round-headed recesses. The stone portion has a high dado in smooth ashlar, separated from an upper section by a molded string course. This upper section has stone blocks laid like large bricks, in a technique known anciently as opus isodomum.
The cella has a pair of vertical rectangular windows flanking the entrance. The latter is a very tall round-headed portal, reaching almost to the roof. This is filled with a glass screen, and is approached by a flight of three modern steps.
The roof itself is a very low tiled cone, in sixteen sectors. It is supported by a wooden ring-beam resting directly on the capitals of the columns, although some of them with damaged capitals have intervening blocks to make up the height.
After the recent restoration, the interior is now quite neat although bare. It is in white up to the open roof, which has two beams in the form of a cross.
There is an internal cornice running round the sides from the entrance, and this bears the epigraph Felix es, virgo Maria, quia ex te ortus est sol iustitiae, Christus deus noster ("You are happy, virgin Mary, for from you has risen the sun of righteousness, Christ our god").
At the back, opposite the entrance, is a large fresco dating from 1475, and in local style. It consists of eleven panels separated by architectural moldings in a trompe-l'oeil false relief. At the top, in a segmental lunette, is God the Father. The main register has ten panels, five smaller ones showing half-length figures over another five with full figures. Of the former, the central is Christ flanked by Our Lady and St John the Baptist, with St Paul to the left and St Peter to the right. The main figures are not so easy to identify -left to right, a young male martyr with a sword and palm, St Andrew the Apostle (?), St Stephen (?), ??, and a monk in a white habit -St Bernard?
Below the fresco is a molded marble frame containing a damaged fresco icon of the Madonna and Child.
The tablet recording the 1475 is extant, and reads:
Sixtus IIII pont[ifex] max[imus], aedem hanc beati Stefani proto martiris, diu incultam et incognitam, instaurant anno iubilei, operante Georgio De Ruvere sacrum aedium urbis curatore.
"Sixtus IV, pope, re-erected this temple of blessed Stephen the first martyr, long unworshipped-in and unknown. Undertaken by Giorgio De Rovere, the curatory of the sacred temples of the city".
Some ancient carved stone fragments found in the restoration are presently being kept in here.
The edifice can be visited on the first and third Sundays of the month, when there is a guided tour at 10:30. This has to be booked in advance -see the tour company's web-page here.
Coarello, P: Rome and Environs, An Archeological Guide, English trans. UCP 2007