Santadi is a comune (municipality) in the Province of South Sardinia in the Italian region Sardinia, located about 35 km southwest of Cagliari and about 20 km southeast of Carbonia. Santadi borders the following municipalities: Assemini, Domus de Maria, Nuxis, Piscinas, Pula, Teulada, Villa San Pietro, Villaperuccio. Starting from a hill next to the small town of Santadi, it is possible to see how the urban development system develops in concentric circles. This fact gave rise to the hypothesis that Santadi is what remains of the capital of the island mentioned by Plato in the third chapter of the Timaeus and in Critias.