The Cittadella of Alessandria (Italian: Cittadella di Alessandria) is a star fort and citadel in the city of Alessandria, Italy. It was built in the 18th century by the Kingdom of Sardinia, and today it is one of the best preserved fortifications of that era. It is one of the few fortifications in Europe still in their original environment, since there are no buildings blocking the views of the ramparts, or a road that surrounds the ditches.

On 10 March 1821, during the Piedmont insurrection, the blue, red and black tricolor of the Carbonari was raised on the Cittadella's bastions by Colonel Ansaldi. This was the first use of a tricolor flag in the history of Italy.
The fortress lies across the river Tanaro in the north-west side of the city of Alessandria. The site is one of the lowest in the Piedmont region with an altitude of about 90 metres (300 ft) above sea-level.
Since its foundation, 1168, the town of Alessandria was always meant to be a border town with a strategic-military vocation. From the 14th century has joined the Visconti of Milan against Monferrato and Asti, with the Sforza then in the 15th century, and consequently under the Spaniards rule after, throughout the 17th century.

The construction of the fortress began immediately after the signing of the Treaty of Utrecht in 1713. The treaty handed ownership of the Citadel from the Spaniards to the House of Savoy. A massive fortification project followed, during which much of Alessandria's town-planning were changed to bolster the fortress's defenses.

In order to meet the needs of defense of the new state of