The Republic of Siena is a state originating from the city of Siena in Tuscany, central Italy.It exists for over four hundred years, from the late 11th century until the year 1555.

At the Italian War, the republic is defeated by the rival Duchy of Florence in alliance with the Spanish crown.

After 18 months of resistance, Siena surrenders to Spain on April 17, 1555, marking the end of the republic.