Fortress of San Leo

The first fortification on the top of the mountain was built by the Romans. In the Middle Ages the peak was bitterly fought over by Byzantines, Goths, Franks and Lombards, and between 961 and 963 it held Berengar II, last king of the Lombard kingdom of Italy, under siege by Otto I of Saxony. Berengar, beaten at Pavia in 961, had taken refuge on the rock more than once.

Around the middle of the eleventh century the Counts of Montecopiolo came to Montefeltro, the ancient name of San Leo, and took from it both the name and the comital title they carried afterwards.

In the second half of the fourteenth century the Malatesta stormed the rocca, and for the best part of a century afterwards the two houses alternated in possession of it, the Montefeltro repeatedly winning it back. In 1441 the very young Federico da Montefeltro took the fort by scaling its walls.

To keep pace with the new military techniques, Federico had the fortress rebuilt, entrusting the work to the Sienese engineer Francesco di Giorgio Martini. The new structure allowed a dynamic counter-offensive: the flanks were laid out to give crossing fields of fire, the sides of the rocca were equipped with artillery, and the approach roads were put beyond the reach of enemy fire by military outposts.

It was one of the palaces held by Federico and his wife Battista Sforza, a fortified, palatial retreat. Renaissance work is stacked against older fabric here: the keep with its square turrets and Gothic entrance is the earlier residential wing, while the round towers and the massive corbelled wall joining them are later, the two of them closing the piazza d'armi between.

In 1502 Cesare Borgia, backed by Pope Alexander VI, took possession of the fortress. On the pope's death in 1503 Guidobaldo da Montefeltro recovered his dominions. In 1516 Florentine troops, supported this time by Leo X and led by Antonio Ricasoli, broke into the town and requisitioned the fort.

From 1527 San Leo belonged to the Della Rovere, and stayed with them until the Duchy of Urbino was devolved to the Papal State in 1631.

Under the Della Rovere the building's purpose changed from rocca to gaol, its cells cut out of the soldiers' quarters. Among the prisoners held there were Felice Orsini and the Palermitan adventurer Alessandro Cagliostro, and the fortress is best known as the place where Cagliostro died. It ceased to be a prison in 1906 and for eight years, until 1914, housed a compagnia di disciplina.

In united Italy the commune of San Leo formed part of the Marche, in the province of Pesaro and Urbino, until 15 August 2009, when it was detached along with six other communes of the upper Valmarecchia in execution of a referendum held on 17 and 18 December 2006; the Marche challenged the transfer before the Constitutional Court, which held the appeal unfounded.

The fortress is protected as Italian national heritage and its rooms now hold an arms museum and a picture gallery. Since December 2014 it has been run by the Ministry of Culture, through the museum authority for Emilia-Romagna that became a regional museums directorate in December 2019. It served as the fictional castle of Leonardo da Vinci in the 1991 film Hudson Hawk.