As showed by excavations of the ruins of castellieri (walls protecting ancient settlements) on the Sienavecchia height, the origins of Stigliano date to Iron Age times.

In the Middle Ages Stigliano was the hub of a network of roads crossing the region, one to Massa Marittima and another following the Rosia river to the Maremma area.

A careful inventory of land properties in 1320, carried out by the Siena authorities for tax purposes, reveals the main source of incomes from this area in middle age: the iron industry.

During this era, Stigliano was an independent commune, owning large areas of woodland and granting permits for allotments to its inhabitants, not only to farmers but also to commercial entrepreneurs and merchants.

However, after the outbreak of the Black Death in 1348 and the subsequent decline of the population, these achievements were neglected and even the revival of agriculture in the 18th century could not compare with the thriving centre in medieval times.

Further on, a farm belonging to the Sienese hospital Santa Maria della Scala was sold to the Placidi family and became an estate called Poderina (rebuilt in neogothic style in the 19th century).