In 978 the monks of Holy Saviour Abbey bought it and it remained in possession until 1153, when the fortress was redeemed by the Papal State and the Anglo-Saxon Pope Adrian IV, being the castle situated in a strategic position of the domain on the via Francigena, it strengthened the fortifications to halt the advance of Federico Barbarossa. In the centuries that followed the castle remained the property of the Papal State and the Republic of Siena. In 1297 the famous "bandit gentleman" Ghino di Tacco takes possession of the castle and there abode for three years, becoming a Robin Hood of our house. Its businesses are remembered by Dante ne"The Divine Comedy" and by Boccaccio in the "Decameron".
In 1300 the fortress back under the Papal State and is the subject of continuous attempts to conquer by the Sienese that if they possessed (with the obligation to pay a heavy annual straight) in 1411, renovating and fortifying the important strategic point. In 1458 the fortress was finally donated to Siena by Pope Pius II (Enea Silvio Piccolomini in Pienza) and thus began a long period of prosperity and stability. During the war between Florence and Siena, the fortress assumed an important role in the conflict, in fact it was the last stronghold of the Republic of Siena. After long years of siege, the Sienese Balzana was lowered on 17 August 1559. It was then Cosimo the Grand Duke of Tuscany to intervene on the old castle, exalting the defensive role and entrusting to the architect Baldassarre Lanci the task of building an imposing fortress.