Siena Cathedral 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. It was the episcopal seat of the Diocese of Siena, and from the 15th century that of the Archdiocese of Siena. It is now the seat of the Archdiocese of Siena-Colle di Val d'Elsa-Montalcino. The cathedral was designed and completed between 1215 and 1263 on the site of an earlier structure.