Erected between the end of the twelfth and the beginning of the thirteenth century, the enchanting duomo of Siena, one of the most splendid examples of Romanesque-Gothic architecture in Tuscany, faces the lovely square bearing its name: the religious heart of the city. Completed in 1377 and consecrated to Our Lady of the Assumption, the huge building, its sides covered with strips of black and white marble, has a monumental and elegant façade divided into two orders; the lower order is opened by three portals with deep splayed jambs, surmounted by refined triangular pinnacles, where between 1284 and 1299Giovanni Pisano created an admirable blend of the architectonic elements and the rich sculpted decoration; instead, the upper order is a splendid example of the flowered Gothic style, ascribable to Giovanni di Cecco and has three spires and a great, central rose window, and contains a fascinating succession of pinnacles, small towers and tabernacles, splendid golden mosaics, executed in the nineteenth century by Augusto Castellani, and a bas relief portraying episodes from the life of the Virgin, the exquisite work of Tino di Camaino. The splendid building is flanked by a tall, black and white striped bell tower which, built in Romanesque style in the thirteenth century, opens in elegant single- and six-light windows and ends in an octagonal in pyramidal spire. The interior, on a Latin cross, opens out solemnly into three grandiose naves, spaced by robust Romanesque columns with black and white marble bands. Elaborate round arches, elegant vaults painted with golden stars on an azure background, and a precious inlaid marble pavement, which was the result of two centuries work characterise the interior, while from 1369 onwards, the all the major Sienese artists including Beccafumi and Pinturicchio, contributed to the decoration. A veritable treasure trove of works of art, the duomo of Siena contains an impressive number of painted and sculpted masterpieces including, in the left-hand transept, the celebrated Gothic pulpit sculpted in white marble by Nicola Pisano in the second half of the thirteenth century, the sixteenth-century Piccolomini altar, the praiseworthy work of Andrea Bregno, the valuable choir window, with episodes from the life of the Virgin, created to a design by Duccio di Buoninsegna, the Renaissance chapel of St. John the Baptist, frescoed by Pinturicchio and Rustichino and adorned with fine statues like the admirable bronze statue of the Baptist by Donatello. The remarkable and sumptuous Piccolomini library, annexed to the duomo should not be missed; founded in 1492 by the cardinal Francesco Todeschini Piccolomini, the future Pope Pius III, in honour of his illustrious uncle Enea Silvio, Pope Pius II, it has a refined marble front, built in 1497 by Lorenzo di Mariano, known as Marrina, and a superb decorations, carried out at the end of the sixteenth century by Pinturicchio with the collaboration of Raphael.