Siena was founded upon a hilltop, approximately 65 kilometres east of the Tyrrhenian Sea and almost 320 metres above sea level in the Chiana mountain range. The city's origins have long been recognized to extend to the Middle Ages, though several earlier historians traced its foundation further back, to either an Etruscan or a Roman settlement. It is only since the mid- 1960s, with the discoveries made by archeologists in the area of Siena, that light has been shed on the early history of the city.

The general history of Etruscan cities in Tuscany has been relatively well established. Around the second half of the eighth century bce the first nuclei were formed in Tarquinia, Cerveteri, Veio, Vulci, Bolsena, Chiusi, Roselle, Vetulonia, Populonia, Arezzo, Cortona, and Perugia. These cities were known as the Dodecapoli (‘twelve capitals’). Several smaller centres were subsequently established, including Cosa, Talamone, Pistoia, Fiesole, Volterra, and Sovana. In the second half of the twentieth century the hypothesis that Siena was also founded by the Etruscans was strengthened by the discovery of archeological remains from the fifth to the fourth century BCE some 12 kilometres from the city (near the town of Murlo). Because of the large size of one of the buildings (70 × 100 metres) archeologists have variously identified the structure as the Temple of Poggio Civitate or even the long-sought shrine known as Fanum Voltumnae, a political sanctuary that functioned as a meeting place and a site for religious ceremonies and games. While debates regarding the nature and identification of the structure are ongoing, the discovery of an Etruscan presence so close to the modern city of Siena supports the proposal that it too was founded by that civilization. This is further confirmed by recent excavations within the city walls that have revealed the existence of two necropoli: the first at San Marco and the second at Campansi, where numerous Etruscan utensils dating from the last quarter of the fourth century bce have come to light.