The monastery, dedicated to the Holy Trinity and later to St. Mustiola, was probably founded in the mid-eleventh century. Its first mention is in a document of 1071, when it was taken under the protection of Pope Alexander II. Around the half of 1100, the monastery joined the Congregation of Vallombrosa, a community of Benedictine monks founded in the early eleventh century. In 1156 wealth and power had grown so much that the abbot Arnolfo, almost in the role of the territorial lord, donated the whole hilltop of Montagutolo by the river Rosia, to Ranieri, bishop of Siena and to three consuls of the municipality, in exchange of an annuity of three pounds of wax. Starting 1224 the monks began, in accordance with the town of Siena, the construction of several, large mills on the river Merse. Next to the monastery had meanwhile risen a castle, whose inhabitants formed one of the municipalities of Siena. In 1333 the castle and the monastery were devastated by troops coming from Pisa. At the end of the thirteenth century a process of slow decline started, due to financial problems. In 1465 the monastery stopped having an independent existence and was attributed to the Episcopal revenue of Siena. The village still offers a medieval atmosphere. An arched portal, that opens the stone walls, leads into a square with an old oven. To the right of the square, through an arch, there is the entrance of the abbey, transformed into a villa in the nineteenth century: on the right side you can see the side of the church, surmounted by an richly craved architrave … you seem to be in the Middle Ages. There is a door that leads into a wonderful cloister. It is perfectly preserved on all four sides and built on three floors, it is certainly one of the most extraordinary and suggestive works of the countryside around Siena. The oldest is the inferior order in small arches on columns, it has an incredible variety of decorations. The above arches are obviously of a later date and they lay on stocky pillars made of brick. The final loggia is made of wood.