Name of Siena cathedral: Duomo di Siena. Siena Cathedral is a medieval church in Siena, Italy, dedicated from its earliest days as a Roman Catholic Marian church, and is 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. Image by BIG ALBERT is licensed under CC BY 2.0.