Siena has had a rich tradition of arts. The Sienese school, a school of painting that flourished in Siena between the 13th and 15th centuries, includes such artists as Duccio, Simone Martini, Pietro Lorenzetti, and Martino di Bartolomeo. You can see the above artists' works, as well as the art by Guido da Siena, (mid-13th century) Domenico Beccafumi, Lorenzo Loto, Domenico di Bartolo in the church of San Domenico and the National Pinacoteca of Siena.
Siena Cathedral, aka Duomo, is a masterpiece of Italian Romanesque-Gothic architecture and a focal point of important ecclesiastical buildings that comprise a museum, baptistry, and crypt. The construction of Duomo started in 1215 and was completed nearly 100 years later, in 1380, that's how much work was put into it. Duomo became one of the most prominent monuments in Italy. The statues of philosophers and prophets adjourning the building are copies from the originals located in the Museo dell' Opera.