Although the buildings located in Piazza dei Miracoli were built at different times, it was a unitary project right from the beginning. The four monuments are connected to each other by an invisible thread that links them to thousands of years of culture. The design of their geometry shows the dialogue between heaven and earth: the Baptistery symbolises birth, the Cathedral and the Bell Tower symbolise life, the Monumental Cemetery symbolises death and resurrection.
The Baptistery of San Giovanni, the largest in the whole of Europe, was entrusted to the architect Diotisalvi, a person about whom no written sources are available and who had designed the monument with the same architecture as the Dome of the Rock in Jerusalem. Its construction, which was entirely financed by the citizens, was later completed by Nicola and Giovanni Pisano. The Baptistery follows the harmonious axis of the other monuments in the square, with which it is perfectly aligned, to the point that, at midday, in every season of the year, the Cathedral does not create a shadow over the Camposanto.
There are two halves to the dome: the one facing the sea has a red tile roof, while the one facing east has lead slates.
The Baptistery inside it has eight columns alternating with four pillars that delimit the central space, where there is an eight-sided baptismal font built by the master sculptor Guido da Como. Nicola Pisano created the magnificent pulpit, a work of great beauty dating back to 1260. The bas-reliefs present inside, tell the story of the life of Jesus, from his birth to his crucifixion and Final Judgment. Once again, the themes of birth, death and resurrection are recurrent.
The Baptistery is devoid of decorations: this permits extraordinary acoustics and, during a visit to the monument, it is possible to listen to this unusual phenomenon. At one time, a ray of sunshine would filter through an opening on the dome, during the spring equinox, illuminating the baptismal font. Today, the opening can still be seen, although it is plugged.