The medieval village of S.Giovanni d' Asso rises in the heart of the 'Crete Senesi' and 'white truffle' territory, it can be reached from Sinalunga [ exit 'Val di Chiana/Bettolle' of A1 ] passing through the SS38 across Trequanda/Montisi or from the scenographic route from Siena, passing across Asciano and the Abbey of Monte Oliveto Maggiore.
From the 1200's onwards San Giovanni d'Asso passed into the secure hands of the most powerful Sienese families: the Buonsignori, Salimbeni and Petroni. The castle was object of debate between the Bishops of Arezzo and Siena, then was sacked by Ghibellines in 1315. Only in the middle of the 15th century the Republic of Siena took direct control on San Giovanni d'Asso.
The old defensive structures around the village, which grew up alongside the castle, have almost completely disappeared, except for a large tower. The Castle is however well preserved and located in the higher part of the town, called 'Borghetto' [Hamlet], its origin dates back to the 13th and 14th centuries.
It was erected by the Sienese architects Agostino and Agnolo di Ventura. The fortified structure, completely built in bricks, consist of two parts, one much older with the characteristic of a fortress with bastionated walls, turrets and some remnants of crenellation, the other with the appearance of an urban palace with single light , mullioned windows with gothic arches and a huge courtyard. It was also used as 'Grancia' of the Hospice of Spedale of Santa Maria della Scala of Siena. In the month of November, the Castle hosts the famous White Truffle Market Exhibit.