Certainly from 1055 - there is a bull of Henry III Emperor of the Holy Roman Empire in this date - the territory of Murlo was the Feud of the Bishops of Siena. They kept their power for 700 years, in spite of all the great historical transformations happening all around (the Siena Repubblic, the Medici dominion, the Grand-duchy of Tuscany). That's why we can say the Middle Ages of Murlo is very long because it lasted untill the French revolution: the legislation and the conservative policy of the Bishop had an enormous influence on the history of this area.
There are many traces of this period in Murlo territory, <castles>, <churches>, <country churches>. The most important is <Murlo Castle>, that was the main centre of the Feud, residence of the Bishop,which is why the small <St Fortunato church> got the rank of cathedral.
The Grand-duke Leopolde of Tuscany decreed the end of the Feud in 1778.