San Giovanni in Fonte

Near the Basilica of San Giovanni Laterano stands a separate building that is the baptistery for the basilica. When it was built, the style of Christian churches usually called for a separate building for baptismal purposes. This particular baptistery was the prototype for many Christian baptisteries throughout Europe.

The structure on the left is the end of an extension of the basilica. The octagonal building in the center is the baptistery. The remnant of a building on the right is an ancient Roman bath building. The St. John Baptistery was said to have been constructed at the direction of the emperor Constantine around 315 AD after he decriminalized the Christian religion. Additions were made over the centuries, the most prominent being the addition of side chapels by Pope John IV in 640 AD.

The eight porphyry columns supporting the architrave were added by Pope Sixtus III around 440 AD. All the paintings in the main chamber are around the theme of the conversion of Constantine. Legend has it that Constantine himself was baptized here. There are too many varied accounts of his baptism to be certain of that though.

The paintings in the upper level of the dome continue the theme of the conversion of Constantine. The ceiling is decorated with symbols of the Barberini family. The inscription around the center ring quotes Genesis LXX: "Spiritus Dei ferebatur super aquas" (the wind of God swept over the water). The columns extending upward from the architrave are white marble.

The baptismal font is, of course, the center of all here. This font made of green basalt is ancient but not the original.

The narthex which was added in 440 AD by Pope Sixtus III has an apse at each end.

The Chapel of St. Venantius was among the additions of Pope John IV in 640 AD.

This painting in the center of the main chamber is by Giacinto Geminiani of the 17th century Baroque period. The painting titled The Vision of the Cross depicts the reported epiphany of Constantine prior to the Battle of the Milvian Bridge in 315 AD. Tradition has it that Constantine, preparing to face the superior army of the co-emperor Maxentius the following morning saw in the heavens a cross and heard the words "In hoc signo vinces!" (In this sign you shall conquer.). Constantine reportedly roused his troops and had them all paint Christian crosses on their shields to prepare for the battle. When the two armies engaged, the smaller army of Constantine easily overwhelmed the main Roman army at the Milvian Bridge and Constantine entered the city as the emperor --- the first Christian emperor.