The suburb of Porrona, in the town of Cinigiano, boasts a small, medieval fortress built by the Sienese between 1100 and 1200 CE. The castle was originally used as the residence of the noble families who came here from Siena. Beginning in the 1300s it served as the residence of the Tolomei and Piccolomini families who shared control of the castle and the adjoining palazzo. The building was modified during the Renaissance, at the beginning of the 16th century, removing a number of typically medieval stylistic elements which have seen been recuperated in a restoration which was carried out at the beginning of the 20th century.
The castle is located in the central piazza of Porrona, near the Parish Church of San Donato, and was built by two workmen. The facade looks out over the piazza of the church, broken at a certain point by the tower which is crowned with crenellations. The interior walls are worth noting: they are finished in stone following the style of the Middle Ages.