Siena Cathedral. Siena Cathedral is a medieval church in Siena, Italy, dedicated from its earliest days as a Roman Catholic Marian church, and now dedicated to the Assumption of Mary. It was the episcopal seat of the Diocese of Siena, and from the 15th century that of the Archdiocese of Siena. It is now the seat of the Archdiocese of Siena-Colle di Val d'Elsa-Montalcino. The cathedral was designed and completed between 1215 and 1263 on the site of an earlier structure. It has the form of a Latin cross with a slightly projecting transept, a dome and a bell tower. The dome rises from a hexagonal base with supporting columns. The lantern atop the dome was added by Gian Lorenzo Bernini. The nave is separated from the two aisles by semicircular arches. The exterior and interior are constructed of white and greenish-black marble in alternating stripes, with addition of red marble on the façade. Black and white are the symbolic colors of Siena, etiologically linked to black and white horses of the legendary city's founders, Senius and Aschius. The origins of the first structure are obscure and shrouded in legend. There was a 9th-century church with bishop's palace at the present location. In December 1058 a synod was held in this church resulting in the election of pope Nicholas II and the deposition of the antipope Benedict X. In 1196, the cathedral masons' guild, the Opera di Santa Maria, was put in charge of the construction of a new cathedral. Works were started with the north-south transept and it was planned to add the main, larger body of the cathedral later, but this enlargement was never accomplished. By 1215 there were already daily masses said in the new church. There are records from 1226 onwards of the transport of black and white marble, probably for the construction of the façade and the bell tower. The vaults and the transept were constructed in 1259-1260. In 1259 Manuello di Ranieri and his son Parri carved some wooden choir stalls, which were replaced about 100 years later and have now disappeared. In 1264, Rosso Padellaio was paid for the copper sphere on top of the dome. A second massive addition of the main body of the cathedral was planned in 1339. It would have more than doubled the size of the structure by means of an entirely new nave and two aisles ranged perpendicular to the existing nave and centred on the high altar. The construction was begun under the direction of Giovanni di Agostino, better known as a sculptor. Construction was halted by the Black Death in 1348. Basic errors in the construction were already evident by then, however, and the work was never resumed. The outer walls, remains of this extension, can now be seen to the south of the Duomo. The floor of the uncompleted nave now serves as a parking lot and museum, and, though unfinished, the remains are testament to Sienese power, ambition, and artistic achievement. Underneath the choir of the Duomo, a narthex containing important late 13th-century frescoes was found and excavated in 1999-2003. The frescoes depict scenes from the Old Testament and the life of Christ. This was part of the entrance of an earlier church. But when the baptistry was built, this under-church was filled with rubble. The narthex is now open to the public. The belltower has six bells, the oldest one was cast in 1149. The façade of Siena Cathedral is one of the most fascinating in all of Italy and certainly one of the most impressive features in Siena. Each of the cardinal points has their own distinct work; by far the most impressive of these is the west façade. Acting as the main entryway to the Duomo proper, it boasts three portals; the central one is capped by a bronze-work sun. Built in two stages and combining elements of French Gothic, Tuscan Romanesque architecture, and Classical architecture, the west façade is a beautiful example of Sienese workmanship. Work began on the lower part around 1284. Built using polychrome marble, the work was overseen by Giovanni Pisano whose work on the Duomo's façade and pulpit was influenced by his father Nicola Pisano. The lower portion of the façade is designed from Giovanni's original plans. Built in Tuscan Romanesque style it emphasizes a horizontal unity of the area around the portals at the expense of the vertical bay divisions. The three portals, surmounted by lunettes, are based on Giovanni Pisano's original designs, as are much of the sculpture and orientation surrounding the entrances. The areas around and above the doors, as well as the columns between the portals, are richly decorated with acanthus scrolls, allegorical figures and biblical scenes.