The picturesque cone-like village perched on a hill (487 m. a.s.l), which spirals around a single narrow road within the remains of the ancient walls, the old houses, palaces and churches and the steps that lead up to the summit of the lower and the fort, preserves the warm blonde colour of the sandstone with which almost all of it is built. Its origins are etruscan as the name testifies, deriving from the etruscan “Petruni”, (or even from the Latin “Praetorium”, and archaeological remains discovered nearby.

In the oldest documents in the Capitulary Archives of Arezzo and the State Archives of Siena is called "Castro Pretorio", while in a consistory document from the Camaldolese annals of 1180 under Pope Alessanaro 3rd it is named “ Pretorio “, (villa or residence ) and S. Pietro‘s church was united in one parish wih S.Andrew at Abbadia Sicille.

Petroio was , as Trequanda , one of the properties of the Cacciaconti della Scialertga since 1175, also under the authority of the commune of Siena . From 1271 a magistrate sent by the Sienese Republic, and administrating from the Palazzo Pretorio, had the authority to expect those considered undesirable.
From the statutes of Siena of 1349 and 1360 it is known that a “mezzo staio “of salt was assigned each resident of the spedale of S. Andrew in Petroio , which was situated in the similarity named church still to found there .

The village became a feudality of the Salimbeni family towards the end of the 14th Century and then of Piccolomini- Bandini, but the return under the Republic of Siena until its fall in 1555 then passing to the Granducato of Toscana . The statute of Petroio was drawn up under Pope Paolo IVth.

Looking to the left over the wall and following the road into the village the little church of St. Andrea can be seen below, seat of the old spedale. Of the former gateway of petroio, long destroyed, remains only a sculpted Templar's cross, partly hidden by a caper plant, of the ancient village walls only a few diminished towers.

Continuing beyond the old terracotta factory with its tall chimney, in a widening of the walls to the left, the romanic church of ST. Giorgio, the oldest in Petroio, in which are to be found canvases of the 17th and 18th century. Further on, still to the left, the ancient Palazzo Pretorio which now houses a terracotta museum. In the similarily named piazzetta St. Pietro and Paolo’s church, with some canvases of unknown 17th and 18th century painters and a lovely oil painting by the Sienese artist Rutilio Manetti (1571-1639), depicting the Ascension with saints and seraphims.

Next door, in the parochial house, is a panel of the Madonna and child by another sienese artisit, Taddeo di Bartolo (1362-1422). Still further ahead on the right is the chapel of the Compagnia del Corpus Domini in which is housed a canvas of the last supper from the 17th Century fort, first residence of the Cacciaconti, then of the magistrate sent from Siena.

At the top of the steps leading to the entrance stands a small terracotta statue of Bartolomeo Garosi, called “il Brandano”. Famous eccentric medieval preacher. Characteristic of the village is the ornamental use of the original and beautiful objects of terracotta still made today by the local artisans and factories.

Travelling along the road from Petroio to Castelmuzio the panorama is wonderful, of woods, vineyards, fields, rows of cypresses and the profiles of Pienza, Montalcino and Monte Amiata. A memorable trip to make at sunset.