A wonderful example of the Gothic style, Siena´s cathedral also known as Duomo di Santa Maria dell'Assunta is located in Piazza del Duomo, facing the Ospedale di Santa Maria della Scala. Most of the cathedral was built in 20 years, starting in 1196 yet other important parts were continued in the following century. The cathedral is part of a magnificent complex formed by itsbaptistry and its bell tower...the three of them paying homage to the Gothic splendour. Beautiful but imposing, the cathedral is admired throughout Italy and worldwide due to its loyalty to the Gothic style.
Twelve steps, in honour of the twelve apostles, lead to the cathedral.
After finishing the construction of the cathedral, the white, green and red marble façade (Picture 1) was left unfinished by Giovanni Pisano when he died. Completion was reached in the 1300s. The two portals in the lower section are topped with lunettes ann Gothic frontons.The gables’ mosaics were added in the 1800s. Giovanni Pisano’s statues in the lower section were replaced by reproductions as the originals are kept in the museum next-door.
In the 14th century there was a project planned, which was never carried out because of the plague, to make the cathedral the biggest worldwide.
To meet Saint Bernardino's wishes, a Sun Symbol, symbolizing Jesus, was added above the main portal in the 1400s. 
Other modifications carried out in the 1800s were the addition of the gold Venetian mosaics fronting the cathedral. In the last century Enrico Manfrini was commissioned to sculpt the bronze doors which replaced the original main portal.
Inside, walls and pillars are striped in white and black matching the exterior. The vaults are blue dotted with golden stars and the nave is bedecked with 172  plaster busts of popes.
The inlaid marble floors were created by various artists and finishing its decoration took 2 centuries. 56 panels are displayed on the floors representing scenes from history and the Bible, such as the She-wolf of Siena and the Wheel of Fortune, and Emperor Segismund Enthroned. Among the artists who left their mark on the floor are Domenico di Bartolo, Domenico di Niccolò dei Cori, Alberto Aringhieri and Domenico Beccafumi. Only for a few days in August are all panels are visible as they are protected and covered for the rest of the year.
The presbitery's high altar is Baldassarre Peruzzi's fine work and the candelabra with angels flanking the altar are Francesco di Giorgio Martini's.
The Gothic 13th century pulpit (Picture 3) made of marble and porphyry was created by Nicola and Giovanni Pisano. Another highlight is Donatello’s bronze Saint John Baptist in a chapel near the north transept.
Among other pieces of art to highlight in the building are: Michelangelo's Saint Peter and the statues of Chigi Chapel by Gian Lorenzo Bernini.
Renaissance artists such as Tino de Camaino, Donatello and Neroccio de Landi were commissioned to create the funeral monuments to Cardinal Riccardo Petroni, Bishop Gioavanni di Bartolomeo Pecci and Bishop Tomasso Piccolomini.
In the left transept is the Chapel of San Giovanni Battista whose pieces of art are Donatello's bronze statue of Saint John, Pinturicchio's frescoes depicting religious scenes as well as secular scenes of Alberto Arighieri's life. 
The Cappella Chigi or Cappella della Madonna del Voto is in the right transept. This eye catching chapel stuns visitors with its gilded cupola by Johann Paul Schor and the San Girolamo and Santa Maria Maddalena statues created by Bernini. Other highlights are Antonio Raggi's Saint Bernardino of Siena and Ercole Terrata's Santa Caterina di Siena, as well as the breathtaking columns, originally decorating the Palazzo Laterano in Rome and the Madonna del Voto executed by the Scuola di Siena.