This historical non-fiction work investigates the integration of Siena into the Medici-ruled Grand Duchy of Tuscany following the fall of the Sienese Republic in 1555. Through detailed archival research, Luciano Rombai examines the administrative, territorial, and political transformations between 1555 and 1609. The study highlights how the Medici state consolidated control over Siena and restructured its institutions, land governance, and civic identity. Combining regional history with broader state-building processes, the book contributes to the understanding of early modern territorial administration in post-Renaissance Italy.