The Abbey of Santa Innocenza in Piana, or more simply the Pieve di Piana as it is called in the area, is located about 3 km away. from Buonconvento and, from the top of the hill where it was built, dominates the valley of the river Stile.
Its history is lost in the mists of time and therefore a veil of mystery surrounds it. It is difficult to attribute a certain date to its construction, some historians, however, would even trace it back to the 7th – 8th centuries. At that time, in fact, there was a great need for the peasant populations to defend themselves from the assaults of the barbarians (this would explain the fortified structure of the building).
Since its establishment, the parish of ss. Innocenti, it was considered one of the richest in the diocese given the extent of its possessions and the amount of income. Its importance then grew over the years thanks also to the treasures brought by the various rectors, who often belonged to wealthy Sienese families. From 1282 the assets of the Pieve di Piana were united with those of the Bishopric and the Bishop of Siena also became Rector of the population of the Val d’Arbia.
In 1398, by decision of the Republic of Siena, the Pieve di Piana was further fortified, as a point of defense against possible attacks by the Florentine troops, which had penetrated the Sienese territory the previous year. The Republic, which at that time did not have sufficient money to buy the building, delegated the purchase to the hospital, which then also took on the burden of the fortification works.
After the renovation, the place had become so safe and welcoming that Pope Paul III, on 7 July 1533, decided to stay there returning from Nice where he had met Charles V of Spain and Francis I of France.