On the Duomo Square, opposite the old hospital of Santa Maria della Scala, rises the huge majestic Cattedrale dell'Assunta (the Cathedral of Saint Mary of the Assumption), a splendid example of the Italian Gothic.
The building, begun in 1230, replaced a previous cathedral of the IX century, entitled Santa Maria. The cupola (or Dome) was added in 1264, but in the 1300s the church was completely transformed: the central nave was raised and illuminated by trifora (three-arched) windows, the façade was worked on by, amongst others, Giovanni Pisano, the chorus was changed, and above all, the transept was widened, in the ambitious attempt to transform the cathedral into the biggest temple of Christianity. Of this last insane widening, begun in the first half of the 1300s and interrupted by the terrible plague of 1348 (as well as by the collapse of some of the structures), there remain traces of the structures effectively built on the left side of the current Duomo: the so-called 'facciatona', the columns of the three naves and a part of the left side, where you can see what is certainly the most brilliant door of the Sienese Gothic. The door opens onto the staircase that leads to the lower Baptistry of San Giovanni.
After the failure of the plan for the New Duomo, work, from then on, concerned the old building. The façade was finished in a gothic style at the end of the 1300s, integrating the part by Giovanni Pisano. The originals of the marble statues (some of which are the work of Pisano), that enrich the façade with depictions of Saints, Prophets, and allegorical Sybils and Animals, are assembled on the ground floor of the Museo dell'Opera.
The dominant theme on the inside of the Cathedral, apart from the wideness of the naves and of the transept (in imitation of the Romanesque Duomo di Pisa), is the colour: the two colour print of the covering, in horizontal strips (the recurring theme of the Sienese 'Balzana') covers the whole of the structure, including the pillars, unifying the richness of the architecture into a homogenous togetherness. The space seems to have been built entirely from colour and light, more than from the solidity of the mass masonry.
The huge masterpiece, not only of Sienese art, on which worked the greatest Sienese artists of the 1400s and 1500s, is the spectacular multi-coloured marble flooring, that covers the whole of the inside of the Duomo like an enormous carpet. Divided into 52 squares, there are depictions of biblical scenes in prevalence, the most famous of which is the Massacre of the Innocents, carried out according to the design by Matteo di Giovanni, in 1482.
In the left transept, we can again admire another famous masterpiece, the Pulpit by Nicola and Giovanni Pisano, certainly the most important work held in the Duomo and considered to be a milestone in the history of art. The three greatest sculptors of the time, the two Pisano and Arnolfo di Cambio, worked together on this work, which is characterised by an astonishing decorative richness (there are almost 400 figures, amongst which humans and animals) and also by the exceptional expressiveness and dramatic force of the sides.
But the Duomo holds another big treasure: the Libreria Piccolomini, a space requested by Cardinal Francesco Piccolomini, archivist of Siena, in order to store the rich collection of books belonging to his uncle, pope Pio II Piccolomini. The room has been fully refurbished; on the walls and ceiling are marvellous frescoes, the work of Pinturicchio, painted between 1502 and 1507. The most important facts about the life of the pope are narrated here, in a scene of striking effect, in very bright colours.
The interior of the Duomo of Siena is often described in superlatives, and what first catches the eye are the striped walls and pillars that continue the black and white stripes of the exterior. Next, the eyes are drawn heaven-ward to the blue-painted vaults adorned with twinkling gold stars. One area worthy of the most extravagant superlatives, however, is the magnificent mosaic floor.
Created over a period of five centuries, the intricate mosaics created in marble were based on preparatory cartoons drawn by leading Sienese artists. Visitors who have already admired the Column of the She-Wolf outside the Duomo should look out for a floor mosaic of the She-Wolf suckling her twins, Romulus and Remus.
Descending below the marble floor, visitors enter the Crypt, an astounding archaeological discovery made only in 1999. Its discovery greatly furthered our knowledge of both the cathedral's construction and 13th-century wall painting.