Fortezza di Mont'Alfonso, Military fortress in Castelnuovo di Garfagnana, Italy.

Fortezza di Mont'Alfonso is a fortified military complex on the hill above Castelnuovo di Garfagnana, begun in 1579 and completed in 1586 to designs by the Carpi engineer Marco Antonio Pasi. Its walls and bastions close the Duchy of Ferrara's border toward the Republic of Lucca. The North Gate opens onto the former «Prigione nuova», the 18th-century prison later turned into a Liberty-style villa by the Bechelli family.

The fortress was built between 1579 and 1586 under Alfonso II d'Este's direction to protect the Duchy of Ferrara's border against threats from Lucca. This project exemplified Renaissance military engineering and became a key defense point for the region during that era.

The central buildings display architectural elements from the 16th century, including the captain's residence, military quarters, and a stone well. These spaces give a sense of how daily life unfolded within the fortress and what purposes each area served.

The fortress is accessible via the Ariosto walking trail and houses offices of the Provincial Administration along with exhibition spaces. Visitors should know the site functions as an active administrative center, so availability may vary depending on events.

In 1942-43 the fortress served as a civilian internment site for about seventy Jewish refugees, including families with children, who integrated into the town. On 4 December 1943 most were arrested, taken to Bagni di Lucca and deported to Auschwitz; only two survived.