The choice to dedicate the city of Florence to St John as its patron dates back to around the 6th-7th century. We have only had certainty about the choice of San Giovanni since the 13th century, ever since the chronicles began to hand down stories telling us about celebrations held in Piazza del Duomo, around the Baptistery, to which the Florentine nobles donated richly decorated candles to burn on the day in celebration of St John. The Baptistery, a temple dedicated to the god Mars in antiquity, was founded between the 4th and 5th centuries AD. The first definite stories found in writing, date back to March 897, describing it as a baptismal font and as a Cathedral. In 1059, Pope Nicholas II consecrated it a Basilica and, in 1128, it became a Baptistery only. This was also the ancient location of "the investiture of knights and poets" as Dante tells us in the 25th canto of Paradise.
The Baptistery is octagonal in shape and conceals mysteries and tales. The Last Judgment is depicted in mosaic above three of the segments of the dome, dominated by the great figure of Christ: beneath his feet, the resurrection of the dead is taking place, on his right the righteous are welcomed into heaven by biblical patriarchs, while on his left there is hell with its devils. The other five segments are divided into a further four horizontal registers, where the figures depicted, starting from the top, are: stories of the Genesis, stories of Joseph, stories of the Virgin Mary and of Christ and stories of St John the Baptist.
A curious fact regarding the great funeral monument is that it contains the remains of Pope John XXIII, whose name was Baldassarre Cossa (1370-1419) and was better known as the antipope, the one who was accused of being a poisoner and of having sold his soul to the devil. Protected by Giovanni di Bicci de' Medici and by Cosimo the Elder, he was deposed during the Council of Constance in 1415.
When leaving the Baptistery, the green and white marble, the beauty of which stands out now, following renovation work, is interrupted by three bronze doors decorated with bas-relief tiles. The South Doors were built by Andrea Pisano between 1330 and 1336, the North Door and the East Door, known as the Gates of Paradise, are the work of Ghiberti and his workshop during the Renaissance period.