Siena Cathedral (Duomo di Siena) 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. Previously the episcopal seat of the Diocese of Siena, from the 15th century the Archdiocese of Siena, it is now that of the Archdiocese of Siena-Colle di Val d'Elsa-Montalcino.
The cathedral itself was originally 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, representing the black and white horses of the legendary city's founders, Senius and Aschius.