The Siena Cathedral may be considered as one of the most beautiful examples of Italian medieval Gothic style. The harmony of exterior and interior finished with marble make it one of the most beautiful cathedrals in the world. And the inlaid marble mosaic floor put it among the masterpieces of world art.

The Siena Cathedral dedicated to the Assumption of Mary is often called simply Duomo. It was built between 1215 and 1263. However Siena masters completed its finishing, both exterior and interior, and especially the mosaic floor only several centuries later.

In the Middle Ages the Republic of Siena competed with the neighbouring Republic of Florence and in 1260 there even were a war between them. The troops of Florence came to Siena and ordered the citizens to open the city gate. But the latter took the keys from all gates, put them on the altar of the recently built cathedral and begged the Holy Mother to protect them. In the Battle of Montaperti the small army of Siena managed to defeat the mercenaries from Florence. After that all rich citizens of Siena held it their duty to decorate the cathedral in return for their salvation.

The cathedral has a Latin cross plan. The construction of the cathedral was headed by the Bernardines who invited two well-known architects, father and son, Nicola and Giovanni Pisano, from Pisa. The architects could harmoniously combine the features of the Roman and Gothic styles.

There are a lot of sculptures and bas-reliefs on the facade of the cathedral. Giovanni Pisano worked at the facade of the cathedral.  The bell tower, which was erected in 1313, is inlaid with white and black-green marble, as the columns inside the cathedral. The pulpit-tabernacle of Carrara marble is a true masterpiece of art. It is ornated with skillful bas-reliefs. The columns of the pulpit are supported by the back of lions from porphyry. 

The floor of the cathedral is the source of pride of the citizens of Siena. It consists of 56 marble slabs with the scenes from the Bible. «The Massacre of the Innocents» by Matteo di Giovanni is one of the most famous scenes depicted on the marble floor of the cathedral. The first marble slabs were put on the floor in 1369. The last marble slabs were put only in 19 century.