In the second half of the fourteenth century the Sienese aristocrat Stricoccio Marescotti, who had dedicated his life to penitence and the care of the sick, turned his small country house on the Capriola Hill into an oratory dedicated to Saint Onuphrius the Hermit, donating it to the Hospital of Santa Maria della Scala. In the early fifteenth century, after having ensured that the Hospital would give the oratory to the Observants, Bernardino began the foundation of the friary, whose church was initially dedicated to the Assumpted Virgin and, after his canonization, to Bernardino himself (1451). He lived here until 1414 and returned several times during his life.
During the fifteenth century, largely on account of the great evangelical activities carried out by Bernardino and of fame that he was gaining in Italy, Siena’s Observant community gradually acquired prestige in the city and importance within the Order.
In 1474, Pier Paolo d’Ugolino Ugurgieri supported the construction of the church, under the supervision of the frati architectori in collaboration with two illustrious architects:
Francesco di Giorgio Martini (who spent the last years of his life at the Capriola and was buried in the crypt) and
Giacomo Cozzarelli, accountable for the sixteenth century additions - twenty years later the construction of the sacristy, of the underlying crypt and the extension of the friary was commissioned to Cozzarelli by the "Prince of Siena" Pandolfo Petrucci.
The building was then reorganized around the cloisters (the Petrucci cloister, the sixteenth century one and the two older cloisters dating to Bernardino’s days) according to the new spatial distribution devised by Renaissance architectural concepts.
During the war of Siena and the siege of the city in the mid-sixteenth century, the friary suffered heavy damage and the subsequent repairs were very modest due to lack of funds.
Between the seventeenth and eighteenth centuries, both the friary and the church were greatly transformed, following Father Celso Maria Billò’s project. The Basilica acquired a new decorative structure, even as a result of interventions on pre-existing works of art and of the inclusion of new ones, including the group by Mazzuoli which was placed on the high altar in 1764.
Already severely tried by the earthquake, the church was deprived of some prestigious works through the suppressions brought on by the Napoleonic laws in 1810, and those following the unification of Italy in 1866.
The air raids of 1944 seriously jeopardized the Basilica which, however, was rebuilt in compliance with the initial model, using the original stonework where possible. The Basilica dell’Osservanza was finally reconsecrated in 1949.