Located in the mid Parecchia valley, San Leo is perched on an imposing rhomboid-shaped rocky cliff whose walls swoop down in the plain below.
Since prehistory the extraordinary chalky-sandstone rock featured the place’s natural conformation’s twofold identity, at first considered as an inaccessible height, and therefore consecrated to divinity, and later, an invincible natural fortress.
Its ancient name was Mons Feretrius, traditionally connected to an important Roman settlement located around a temple consecrated to Jupiter Feretrius.
The first people to have inhabited these lands, and most probably the cliff itself, were Umbro-Sabelli populations which were followed by Senon Gauls. Not much can be said about the before mentioned Roman settlement, but a sure fact is that since the III century Romans built a fortification gripped onto the highest top of the mountain, which they need not equip with surrounding walls because of the cliff’s natural inaccessibility.
Towards the end of the III century, Leone and his partner Marino reached the Montefeltro area from Dalmatia. They were credited the merit of spreading Christianity which diffused in the surrounding area and led to the birth of the Montefeltro Diocese.
Leone is traditionally considered the first bishop of Montefeltro, even though the foundation of the Diocese dates back to a later time, probably between the VI and VII century to a time when San Leo was upgraded to being a town. The first bishop to have be in records dates back to 826.
From then, the name Montefeltro indicated both the fortress-county town and the whole ecclesiastic region which comprised the Marecchia valley and the neighbouring Foglia and Savio.
On Leone’s death, around 360 A.D., his body was laid to rest in a stone sarcophagus, the lid of which is preserved to date in the Duomo, whereas in the spot he used to retreat in prayer now stands a parish church.
In the VI century San Leo became an organised hamlet, stronghold of Procopio di Cesarea.
In  538, at the time of Goth invasions, the king of the Goths, Vitige, placed a guard of five hundred men, which shortly after, following the defeat of Bellisario, they were forced to give to the Byzantines. Soon enough the whole region was occupied by the Lombards who, in turn, were defeated by Pippin, king of the Francs, who gave it to the Church.
In the X century, after having been beset and comprised in the territories of Ottone I of Germany, the town was once again handed over to the Church.
From year 1000, as a tribute to the patron saint, Leone, the town was renamed San Leo. In 1014 German emperor, Enrico II, attempted to move San Leone’s body to Germany. According to tradition the horses towing the cart, approaching Voghenza near Ferrara, took fright, forcing Enrico II to leave there the Saint’s body which was renamed San Leo di Voghenza.
With the enthronement of Fredrik I of Swabia, the Montefeltro region became fief of count Antonio di Carpegna, a descendant of the Montecopiolo branch. The Montecopiolo esquires first were advanced to counts of Montefeltro and afterwards to counts (1226) and dukes (1443) of Urbino.
The first count of Montefeltro, of whom reliable sources are available, is Montefeltrano (1135-1202), an outstanding political and military figure, who extended his dominium to the fiefs of Urbino, Pesaro and Rimini. His successor was Montefeltrano II (1195-1253). On 8th May 1213, during the celebrations for his investiture to knight, St Francis of Assisi, who was passing, stopped to assist to the inauguration and preached a sermon on the words of a love song known in those days: "tanto è il bene che io m'aspetto che ogni pena m'è diletto" (so much is the love I expect in return that any sorrow is dear to me, trans.).
Count Orlando de' Cattani, esquire of Rocca di Chiusi in the Casentino area, was so impressed by the saint’s words that he gave him Mount of La Verna, where later Francis received the sacred stigmata.
In1226, Fredrik II of Swabia gave Bonconte and Taddeo of Montefeltro the Urbino county, where they moved to in 1234. Due to this passage the San Leo county achieved an administrative autonomy, with the institution of the Feretrana province of which San Leo was the county town until 1816.
In 1479 during the seigniory of the Montefeltro, the fortress was embellished and the medieval tower, defended by the square Malatestian towers, was definitely redesigned on Federico da Montefeltro’s request by Siena architect, Francesco di Giorgio Martini.
With the accession of the counts of Montefeltro, who were popular for their deftness with arms and their ability in politics and patronage, contrasts with their neighbours, the Malatesta and, later, the Faggiolani and Cesare Borgia, intensified.
When Guidobaldo da Montefeltro’s died (1508), the family became extinct and the dukedom was handed over to the nephew, Francesco Maria I Della Rovere, an outstanding impulsive and impetuous warrior and man of politics.
Upon the death of Pope Giulio II Della Rovere’s (1513), his successor, Leone X de' Medici exploited cardinal Alidosi’s murder by Francesco Maria I in Ravenna, in 1511 succeeding to giving the dukedom to his nephew Lorenzo de' Medici.
In 1516 Lorenzo de' Medici, after months of fierce fights managed to take over San Leo. These battles were so gory and vicious to be remembered by Guicciardini, who was among the commanders of the assaulting troops, in his records and immortalised by Vasari and still displayed in palazzo Vecchio in Florence.
Following Lorenzo de' Medici’s death (1519), Leone X was forced to entrust the Feretran county, with San Leo as its county town, to the Florentine Republic. The construction of the palazzo Mediceo to host San Leo and Montefeltro’s governor representing the Florentine Republic date back to that time.
San Leo returned in the Della Rovere’s hands in the person of Francesco Maria II, who built palazzo Roveresco and extended the Medicean one, adding the theatre.
When he died in 1631, in the absence of male offspring, the dukedom was handed over to the Church which ruled it directly until it was comprised in the Kingdom of Italy in 1860.
Since the XVII century the fortress lost its fortalice character and was made-over into a prison. In  1791, the prison of San Leo fortress, hosted Giuseppe Balsamo, known as Alessandro Conte di Cagliostro.
Born in Palermo in 1743, as a young man he lived a hand to mouth existence and became a popular character with the masons of the time.
His fame as an alchemist and heeler reached the most important courts in Europe where he could easily liaise with the leading figures of the time: at the court of Versaille he met powerful cardinal Rohan who involved him in the mysterious affaire du collier, a plot which led to the slander of queen  Marie Antoinette and paved the way to French revolution; he also challenged openly the Church establishing in London a guild based on the Egyptian rite, taking on the title of "Gran Cofto".
The Church passed death sentence blaming him for heresy and mutinous activities. This was later commuted by pope Pio VI in life conviction in the prisons of San Leo fortress, where he was to die on 26th August 1795, taking all the secretes of a restless and adventurous life to the grave. 

Monuments