The Cittadella is a large fort in the city of Alessandria in Piedmont, Northern Italy. Currently, it stands as one of the best-preserved fortresses designed in the modern era.

The construction of the star fort of Alessandria began in the early 18th-century, when, after the War of the Spanish Succession, the House of Savoy took control of the city. The fort, part of a larger defense system all around the domains of the Savoy family, was built starting in 1732 at the expense of the former neighborhood of Bergoglio. The result was a large, six-bastioned fortress surrounded by a moat and protected by more fortifications.

The first test for the new fort came in 1745 when it resisted the French and Spanish siege of Alessandria for seven months during the War of the Austrian Succession. During the Napoleonic invasion of Italy, the fort was controlled by the French and was sieged by the Austro-Russian army in 1799. After this battle, the fort was expanded to become one of the main military installations of the French empire. In 1814, the Austrian army captured the fort and transferred it to the Kingdom of Sardinia.

In 1821, the garrison of the Cittadella mutinied marking the start of the Piedmont Insurrection and the tricolor of the Carbonari flag, the revolutionary group fighting for the unification of Italy, was raised on the fort. The insurrection quickly spread to all Piedmont, becoming the first large rebellion calling for Italian unification, a pivotal moment in the Risorgimento.

The rebellion was suppressed by the Austrians who occupied the fortress until 1823. It was later the site of a battle between Sardinia and the Austrian Empire during the Italian Wars of Independence. Mostly spared by World War II bombings, the fort remained in use until 2007 and is now a museum.