Rome: San Giovanni in Fonte (Lateran Baptistery)

The San Giovanni in Fonte or Lateran Baptistery.

San Giovanni in Fonte is the name usually given to the octagonal baptistery next to the cathedral of San Giovanni in Laterano, the seat of the Pope as Bishop of Rome. The story of this great basilica is well-known. After his victory over his rival Maxentius at the Milvian Bridge in 312, the emperor Constantine (306-337) disbanded the Praetorian Guard because it had fought for his opponent. This included dissolution of the horse guards, the equites singulares Augusti, and the donation of the estate on which their base was built to Rome’s Christian community. The Christians, encouraged by the emperor’s favourable treatment of their religion, then built a cathedral dedicated to Jesus Christ the Saviour, which was later co-dedicated to the two Giovannis: Saint John the Baptist and Saint John the Evangelist. The basilica of the Saviour was consecrated in 324.

There seems to be consensus among historians that the baptistery next door, also known as the Lateran Baptistery, was built during Constantine’s reign as well, perhaps between 320 and 330, so slightly later than the basilica. It quickly became a model for other baptisteries in the Roman Empire, for example those in Ravenna. It seems rather unlikely that the emperor himself commissioned the building, but the claims that he provided it with valuable items – a porphyry font, decorations made of gold and silver – are quite plausible. The Constantinian baptistery seems to have been built into one of the rooms of a bathhouse from the second century, and a fair argument has been made that the pool in this room was already in use for baptisms (by full immersion) in pre-Constantinian times. The baptistery we see today is the result of many restorations and modifications throughout the centuries. It is not a single building, but more of a complex of buildings comprising the actual baptistery, several small chapels and one large chapel – the one dedicated to Saint Venantius – that in practice serves as a parish church.

Original entrance portico.

In this post, I will discuss the individual elements of the complex:

  1. The baptistery itself;
  2. The Chapel of Saint Venantius;
  3. The Chapels of Saint John the Baptist and Saint John the Evangelist;
  4. The Chapels of Secunda and Rufina and of Cyprianus and Justina.

1. The baptistery

The Constantinian baptistery was probably stripped of its precious metals during one of the Sacks of Rome in the fifth century, either after the Goths (in 410) or the Vandals (in 455) took the city and looted it. In any case, the gold and silver statues that Constantine is said to have donated are long gone. The baptistery was remodelled significantly in that same fifth century, in a project started by Pope Sixtus III (432-440) and then presumably continued by his successors Leo the Great (440-461) and Hilarius (461-468). One of the modifications attributed to Sixtus is the addition of a portico to the south side of the baptistery, where the original entrance used to be; the building is now entered from the north, at what was originally the back of the baptistery. One can nowadays only admire the portico with its large porphyry columns from the inside. It is regretfully no longer possible to walk around the baptistery; to the south of the complex there is a private car park and a private road that goes around the cathedral. Access is blocked by a gate.

Interior of the baptistery.

Inside the portico, Pope Anastasius IV (1153-1154) had two chapels constructed which are currently dedicated to Saints Secunda and Rufina and to Saints Cyprianus and Justina. I will discuss these chapels below. From the portico, we turn around again and re-enter the baptistery itself, which acquired its present appearance in the sixteenth and seventeenth century. The original Late Antique dome proved to be beyond repair and was demolished in 1540 and subsequently replaced. The fifth century mosaics that adorned it where unfortunately lost. Pope Gregorius XIII (1572-1585) then added the current baptismal basin, made of green basalt and certainly of ancient origins. The basin was surrounded by a balustrade. As by this time baptism by affusion had replaced baptism by full immersion, the basin replaced the much larger Late Antique baptismal pool (for a similar development, see the baptistery in Florence).

More changes were made in the seventeenth century, starting with a restoration initiated in 1625 by Pope Urbanus VIII (1623-1644). The project included changes to the ceiling and dome from the previous century and the provision of frescoes for the walls and the drum of the dome. These frescoes, showing scenes from the life of Constantine, still dominate the baptistery. They were executed by several artists under the direction of Andrea Sacchi (1599-1661). The fresco work was completed by 1648. The restoration project was then continued by the famous architect Francesco Borromini (1599-1667). Borromini had already been commissioned to work on the interior of the cathedral of San Giovanni next door. He was subsequently employed by Pope Alexander VII (1655-1667) to work on the baptistery as well. If we stand outside the baptistery, we can admire a roofline frieze added by Borromini. It features Alexander’s coat of arms, a set of mountains with a star combined with the oak tree of the Della Rovere family (see Rome: Santa Maria del Popolo).

Constantine’s Vision of the Cross by Giacinto Gimignani (1606-1681).

Borromini added the colourful marble floor and the marble walls surrounding the baptismal font. The font has a bronze cover by Ciro Ferri (1634-1689) which depicts the baptism of Christ on one side, and that of Constantine on the other. The space surrounded by the balustrade can be entered from the north and from the south. The floor – i.e. Borromini’s marble floor – is lower than the floor of the baptistery, and although baptisms by full immersion are a thing of the past, the whole arrangement is clearly intended to recreate the experience of the ancient baptismal pool that used to be here. Inside this pool are two bronze deer from a restoration ordered by Pope Paulus VI (1963-1978). And while the deer are very modern, the huge porphyry columns surrounding the balustrades are from Constantine’s days, although they are probably not in their original position. The entablature above the columns is also from Late Antiquity. So all in all, what we see today is an interesting mix of old and new.

As a final thought, beware of the persistent myth that the emperor Constantine was himself baptised here. He was not. Although medieval Christian propaganda liked to claim that the emperor was baptised by Pope Sylvester (see Rome: Santi Quattro Coronati), there is no truth in this story whatsoever. Constantine certainly gave preferential treatment to Christians and may have been a de facto Christian for years, but the fact remains that he was only formally baptised in 337, on his deathbed. The event took place not in Rome, but in Nicomedia in present-day Turkey. The priest involved was certainly not the Pope, but a man named Eusebius of Nicomedia, archbishop of Constantinople.

Baptismal font.

2. The Chapel of Saint Venantius

Construction of the Chapel of Saint Venantius is usually attributed to Pope John IV (640-642). John was a native of Zadar, in what is now Croatia and was then called Dalmatia. At the time of his pontificate, pagan Slavs were threatening the Christian coastal communities there, so he brought the relics of several Christian Dalmatians to Rome. Saint Venantius, also known as Saint Wigand, was said to have been a bishop of Salona (modern Split), but his origins are rather obscure and not much about his life is known. Nevertheless, Pope John seems to have known who he was and dedicated the chapel to him. Since John’s pontificate was rather short, the chapel and especially the splendid mosaics had to be completed under his successor Pope Theodorus I (642-649).

The Chapel of Saint Venantius.

I personally consider the Chapel of Saint Venantius to be the highlight of the complex, better even than the baptistery proper. The walls are mostly undecorated, so the true treasures of the chapel are the mosaics of the conch of the apse and of the triumphal arch. Unfortunately, a 1674 restoration by Carlo Rainaldi (1611-1691) led to the instalment of a large aedicule or altar screen which blocks the view of a large part of the apse mosaic. We can give Rainaldi credit for re-using the beautiful fifth century marble columns in his new aedicule, but the decision to make the object so large that it effectively obstructs the view of the mosaic behind it was rather stupid in my honest opinion. Part of the aedicule is a fourteenth century depiction of the Madonna and Child, which serves as an altarpiece.

Apse mosaic. On the far left and right, you can just see Pope John IV (left) and Pope Theodorus I (right).

Take your time to walk over to the sides and peek behind the altar screen. The conch mosaic shows a large bust of Jesus Christ in the clouds, flanked by two angels. Christ is making the sign of the benediction. Below him is the Virgin Mary holding out her arms in the orans position. On her left – the viewer’s right – are Saints Peter, John the Baptist and Domnius, as well as Pope Theodorus. Domnius is said to have been one of the first bishops of Salona. The cathedral in modern Split, Croatia, is named after him. Venantius may have been either his successor or his predecessor; this is far from clear, but it hardly matters. Venantius can be found on the other side of the Virgin. He is depicted between Pope John IV, who is holding a miniature model of the chapel, on the left, and Saints John the Evangelist and Paul on the right.

From left to right: Saint Venantius, Saint John the Evangelist, Saint Paul, the Virgin Mary.

Dalmatian saints.

The triumphal arch features several saints who were no doubt famous in Dalmatia, but whose names hardly ring a bell here in Rome. They are all labelled, so you can check out their names for yourself. The top part of the mosaic shows the symbols of the four evangelists and the cities of Jerusalem and Bethlehem. The local parish – the Parrocchia dei SS. Salvatore Santi Giovanni Battista ed Evangelista in Laterano – now uses the chapel as a parish church instead of the cathedral. Weddings are also held here.

3. The Chapels of Saint John the Baptist and Saint John the Evangelist

The baptistery has two small side chapels. There used to be three chapels, but the one dedicated to the Holy Cross was regretfully demolished in 1587. That leaves us with a chapel dedicated to Saint John the Baptist on the right and one dedicated to Saint John the Evangelist on the left. Both were constructed during the pontificate of Pope Hilarius (461-468). His name is mentioned above the entrances to both chapels. The Latin text on the entablature above the doors to the Chapel of Saint John the Baptist for instance reads: HILARVS EPISCOPVS SANCTAE PLEBI DEI.

Chapel of Saint John the Baptist.

The Chapel of Saint John the Baptist is famous for its set of fifth century bronze doors. These used to make a very special musical sound when opened or closed, but apparently this sound was lost after a 1993 Mafia bombing shook the building on its foundations. I have twice visited the baptistery in recent years and have unfortunately always found the chapel closed to the public. One can, however, peek inside through the bars of the gate. The current interior of the chapel dates from 1780 and is the result of a remodelling by one Giovanni Battista Ceccarelli. The chapel has a bronze statue of Saint John the Baptist which was made by Luigi Valadier (1726-1785). His son Giuseppe Valadier (1762-1839), an architect, is perhaps more famous (see Rome: San Lorenzo in Damaso).

The Chapel of Saint John the Evangelist on the other side seems to be closed to the public as well. I got the impression that it is now used as a sacristy for the parish. Apparently a fifth century mosaic and some very old Cosmatesque artwork can be found in here. If you take a look at the first image in this post, you will be able to see the exterior of the chapel on the left.

4. The Chapels of Secunda and Rufina and of Cyprianus and Justina

Pope Sixtus III’s fifth century portico had an apse on either side. As was already mentioned above, Pope Anastasius IV (1153-1154) had these converted into proper chapels. These were in turn given a Baroque appearance in the seventeenth century when Borromini worked on the portico during a project initiated by Pope Alexander VII (1655-1667). The Chapel of Saints Cyprianus and Justina is the more interesting of the two. Its fifth century apse mosaic has been largely preserved, although parts of it have been repainted, which looks a bit daft. The mosaic features vine scrolls, jewelled crosses, doves and a Lamb of God.

5th century apse mosaic.

The chapel on the other side is dedicated to Saints Secunda and Rufina, two local martyrs from the third century of dubious historicity. Their relics were deposited here in 1153. The chapel used to have a fifth century apse mosaic as well, but this was lost in the eighteenth century. Neither of the two chapels is usually open to the public, but I cannot say this is a big loss.


  • Capitool Reisgidsen Rome, 2009 Dutch edition, p. 183;
  • Luc Verhuyck, SPQR. Anekdotische reisgids voor Rome, p. 251-252;
  • The baptistery on Churches of Rome Wiki.


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