Diotisalvi’s work
The current layout of the Baptistery, in its basic lines, dates back to Diotisalvi, who directed the erection of the building from 1152 to around 1180 (according to the ordinary calendar) at least up to the top of the arches of the first order, including the interior pillars and columns, except the capitals. He presumably designed the accessible loggia on the second order, which is perfectly in tune with the one on the façade of the Cathedral. His design retained the civic and political inspiration that had been at the base of the foundation of the Cathedral. The theme of the holy wars lived in the very shape of the Baptistery, which had to bring to mind that of the Holy Sepulchre. Consistent with Diotisalvi’s language is the decoration of the main door, which has a strong Byzantine influence, usually dated to 1200 by comparison with dated works made by the same artist. The eastern door of the Baptistery is more richly decorated, as it was the main entrance to the building, located just in front of the main door of the Cathedral, their styles conversing with each other.
Nicola and Giovanni Pisano
Around the mid-XIII century, the building of the Baptistery underwent a new surge, as shown not just by its style but also by an inscription on the outer wall of the women’s gallery, which says: "anno domini MCCLXXVIII aedificata fuit de novo". So we are in the month of March of the year 1277 according to the ordinary calendar (March 1278, according to the Pisan calendar), and this is the end of a building stage. The resumption of work is to be related to the authoritative figure of Archbishop Federico Visconti, who in those years revoked the Pope’s interdict that had fallen on the city, which had compromised itself by adhering to the Empire. The baptismal font and the enclosure around the presbytery, made in 1246 by the Lombard artist Guido Bigarelli, were followed by the resumption of the building work, with the coming of Nicola Pisano who, along with his son Giovanni, would deeply renew Diotisalvi’s construction. Nicola erected not just the pulpit (1260), which would immediately establish itself as a model for all such pieces, but also crowned the arches of the outer open gallery with a solemn procession of busts, enclosed within an intricate tabernacle-like construction, also enriched by figures, which was then completed by his son Giovanni. The latter probably also made the second row, with large spans at intervals framed by tympanums.
Cellino di Nese
The third and last stage in the building of the Baptistery was carried out by Cellino di Nese, who was appointed Capomaestro, or Master Mason, in 1361. Extremely important for the understanding of the succession of events is a deed dated September 1360, under which several stone-cutters, including Cellino, committed themselves with Lupo Aliotti, canon and treasurer of the Opera di San Giovanni, to complete the building. Appointed to provide Carrara marble "to build arches and windows for the Church of Saint John”, Cellino was actually about to complete the erection of the outer wall and would then go on to complete the women’s gallery that opens on to the central area and build the bold two-domed covering. In the two years 1384-1386, the Baptistery must have already looked as it does now; Antonio Veneziano portrays it, with its dome and the smaller dome on top, in one of the Storie di San Ranieri frescoed in the nearby Monumental Cemetery.
