Fortezza di Montecristo, Coastal fort on Monte della Fortezza in Portoferraio, Italy

Fortezza di Montecristo is a ruined coastal fort at the summit of Monte della Fortezza, the highest point of the island of Montecristo (645 m), in the municipality of Portoferraio. Its wall structures rest irregularly on granodiorite, adapting to the orography of the peak, and the surviving remains suggest the size of the defensive complex. It was once mistakenly believed to be a Roman temple to Jupiter.

A first structure was probably built in the first half of the 13th century under the Republic of Pisa. Jacopo III Appiano rebuilt it in the 1460s to resist pirate raids, choosing the island's highest point for lookout and defence. The island was then nearly abandoned, and the fortress fell into ruin.

The fortress remains reflect the military architecture of medieval Tuscany, incorporating both defensive capabilities and strategic observation points over surrounding waters.

Montecristo is a strictly protected nature reserve and can only be visited on authorized guided excursions, so access to the fortress ruins depends on such permits. The climb to the summit at 645 m is steep and exposed, with no facilities or shelter along the route.

Before archaeology identified it as a medieval fortification, the ruins were long mistaken for a Roman temple dedicated to Jupiter. The walls sit on granodiorite, the same rock that forms the summit of Monte della Fortezza at 645 m, the island's highest point.