San Giovanni in Fonte, Rome

San Giovanni in Fonte (also known as the Lateran Baptistery) is an early Christian baptistery located next to St. John Lateran and the Lateran Palace in Rome.

Built by Constantine the Great in 315, the ancient structure is one of the oldest Christian buildings in Rome and the oldest baptistery in all of Christendom. It provided the model for later versions, including the famous Byzantine baptisteries at Ravenna.


History of San Giovanni in Fonte

Excavations beneath the baptistery have revealed remains of a 1st-century Roman villa and an early-2nd-century bathhouse. The bathhouse was completely rebuilt a century later.

In 315, Emperor Constantine the Great built a baptistery on this site to serve the adjacent cathedral of St. John Lateran, also built by him. Popular medieval legend had it that Constantine was baptized here by Pope Sylvester, but in fact he was baptized on his deathbed by an Arian bishop in 337.

Churches did not contain their own baptisteries at this early date, and San Giovanni in Fonte was the only place to be baptized in Rome until the late 300s. At that time, baptisms were held only at Easter and usually after a period of instruction.

By the end of the 4th century, increasing numbers of Christians led to many more baptisms, which in turn led to baptisms being performed throughout the year and baptisteries being built into churches. Thus free-standing baptisteries like this one stopped being built, and San Giovanni in Fonte itself came to take on the functions of a church.

In the 5th century, Constantine's original baptistery was remodelled by Pope Sixtus III (432-40) in a similar style as the Mausoleum of Santa Costanza, including the addition of a narthex.

A few decades later, Pope Hilarius (461-68) added side chapels dedicated to John the Baptist and John the Evangelist.

Pope John IV (640-42) added the Chapel of St. Venantius, the largest of the three side chapels. John IV was one of the first popes to transfer martyrs' bones to churches in Rome. He brought the remains of Venantius, Anastasia and Maurus from Dalmatia to place in his chapel. A few years later, under Pope Theodore I (642-49), the chapel was decorated with mosaics.

The baptistery was restored under Pope Hadrian III (884-85) and also in the 12th century. A major redecoration of the interior in the 17th century accounts for the unfortunate loss of the ambulatory mosaics and the covering of most of the marble revetment. More recently, the baptistery was fully restored after damage by a car bombing in 1993.

What to See at San Giovanni in Fonte

The brick exterior of San Giovanni in Fonte is entirely original - the walls of the baptistery are from the time of Constantine and those of the chapels are from the times of the popes who built them (5th and 7th century).

The southeast entrance at the back of the building includes the exterior of the narthex built by Pope Sixtus III (432-40), which incorporates two beautiful porphyry columns and a Roman architrave. Inside, there is an apse at each end.

The right apse in the narthex has a 5th-century mosaic of vines in gold and green set against a deep blue background. At the top of the mosaic are six golden crosses, the Lamb of God, and four doves. At the top of the wall left of the apse is a fragment of the 5th-century marble revetment that once decorated the baptistery interior.

The narthex contains a chapel dedicated to Cyprian and Justina (a.k.a. Secunda and Rufina), two martyrs with a romantic story. In a legend dating from the 4th century or earlier, Cyprian was a sorcerer at Antioch who tried to use magic to win the heart of Justina, a young Christian girl. He failed and became very depressed, but after observing a church service he asked to be baptized. He and Justina were subsequenly married, and later martyred.

Nothing from Constantine's time remains inside the octagonal baptistery, but some features from Sixtus III's remodeling in the 430s can be seen: primarily the eight porphyry columns that support an architrave and eight white marble columns.

The architrave bears famous distichs, attributed to Sixtus III's archdeacon, who later became Pope Leo the Great (440-61). The distichs describe 5th-century baptismal doctrine, which has been beautifully translated as follows:

In the center of the baptistery is the baptismal font, which is ancient but not the original, which would have been a large octagonal font. The present font is made of green basalt and bears bas-reliefs of the baptism of Christ and the baptism of Constantine.

The Chapel of St. John the Baptist (461-68), on the southwest side of the baptistery, still has its original pavement. The highlight is the doors, which are said to be made of a mix of bronze, silver and gold and were once thought to have come from the Baths of Caracalla. They produce a powerful musical tone when opened, especially during the hotter months.

The Chapel of St. John the Evangelist (461-68), on the northeast side of the baptistery, still has its original ceiling decoration: a fine mosaic of the Lamb of God surrounded by a wreath divided into sections representing the four seasons, each with specific fruit and flowers.

The large Chapel of St. Venantius (640-42), positioned on the northeast corner between the Chapel of St. John the Evangelist and the narthex, is especially notable for its mosaics (642-49). The apse mosaic centers on John the Baptist and John the Evangelist, a reference either to the baptistery's other chapels or to St. John Lateran next door.

At the top center of the apse is a bust of Christ, with his right hand in the Greek gesture of blessing, on a gold background. He is flanked by angels, with their arms stretched towards him and wearing cloaks bearing the letter H for Johannes (John).

Below, the Virgin Mary stands also in the gesture of prayer, supported by four figures on each side. On her right are St. Paul, St. John the Evangelist, St. Venantius and Pope John IV (who holds a model of his chapel). On her left are St. Peter, St. John the Baptist, an unidentified martyr, and Pope Theodore I (who commissioned the mosaic; he holds a casket).

The row of figures flows onto the triumphal arch, with four more saints on each side. All shown with haloes but very individualized appearances, these are portraits of the martyrs whose relics Pope John IV brought from Dalmatia.

The semicircle around the arch is covered in a mosaic pattern of small crosses in roundels separated by floral decorations. Square panels at either end of the triumphal arch contain depictions of Jerusalem and Bethlehem. Between these are two more panels with the symbols of the Four Evangelists.

A mosaic inscription in the apse (somewhat obscured by a canopy) reads:

Steps on the right-hand side lead to remains of the 3rd-century bathhouse that once stood here, including its mosaic pavement.

Quick Facts on San Giovanni in Fonte

Site Information
Names:Battistero Laterano · Battistero Paleocristiano di San Giovanni in Fonte · Lateran Baptistery · San Giovanni in Fonte · St. John at the Font
Categories:churches; baptisteries; World Heritage Sites
Dedication: St. John the Baptist
Status: active
Visitor and Contact Information
Coordinates:41.886169° N, 12.504319° E
Address:Piazza di San Giovanni in Laterano
Rome, Italy
Hours:Daily 7-12:30, 3:30-7:30pm
Lodging:View hotels near San Giovanni in Fonte
Note: This information was accurate when first published and we do our best to keep it updated, but details such as opening hours and prices can change without notice. To avoid disappointment, please check with the site directly before making a special trip.


  1. Personal visit (exterior only; July 2006).
  2. Matilda Webb, The Churches and Catacombs of Early Christian Rome: A Comprehensive Guide (Sussex Academic Press, 2001), 45-48.
  3. Rough Guide to Italy, 7th edition (2005), 768.

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Map of San Giovanni in Fonte, Rome

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