The precise year when the oldest castle in Bazzano was built is not known. No traces of it remain. Nevertheless, in a document dating back to 1019, The castrum of Bazzano is mentioned, referring to the building of castles in the 10th century.
In 1038, the Bishop of Modena granted the Bazzano curtis to the Marquis Bonifacio di Canossa, father of Matilda.
After Matilda's death in 1115, the court and castle at Bazzano reverted to the Bishop of Modena. The castle was later fought over by the cities of Modena and Bologna, in a struggle to define their borders.
After a failed siege in 1228, Bologna succeeded in conquering Bazzano in 1247; the Bazzanese had to abandon the castle, being free to choose whether to move to Bologna, Modena or some other area. In 1250, the castrum of Bazzano, including the walls and the buildings, was completely dismantled and the stones were transported to Monteveglio for the construction of a tower-house for Bologna officials.
At the end of the 13th century, Azzo VIII d'Este, Marquis of Ferrara, Modena and Reggio, began his expansion to the detriment of the Bologna territory and, supported by Romagna Ghibellines, undertook the construction of a new castle. In 1296, after a long siege, Bologna succeeded once again in taking possession of the castle, completing the construction. Bologna's victory was definitively sanctioned by an award from Pope Boniface VIII in 1299 at the announcement of the jubilee: in recognition, Bologna dedicated a statue of the Pope in gilded copper made by the goldsmith Manno from Siena, showing the pope in an act of benediction.
The construction work was completed in 1310: the new structure included a tower and a building next to it, which today make up the southern side of the internal courtyard of the Rocca, the walls and two keeps: one of the two keeps was soon knocked down since it became a pro-Modena stronghold, and in its place in 1317, the existing clock tower was built.
For the entire 14th century up until the first half of the 15th century, the ownership of the castle fluctuated between Bologna, the Visconti and the Papal State. In 1473 the palatium and surrounding land was given to Giovanni II Bentivoglio, lord of Bologna. The Bentivoglio family made substantial changes to the building, incorporating the late 13th century military structures into a noble residence, one of the "delights" that the Bentivoglio family owned in the Bologna area and where they resided occasionally for holidays and vacation periods. In 1490 the work was completed and the building remained the property of the Bentivoglio family until 1506 when they were expelled from Bologna.
In 1508 the city of Bologna named the castle of Bazzano the headquarters of one of the three "captaincies of the montagna", a wide territorial area comprising the 23 municipalities in the Lavino and Samoggia valleys. Inside the Rocca were the civil and penal court of the captaincy, the administrative offices, prisons and the residence of the captain and armsmen.
In 1799, Ugo Foscolo was imprisoned there; at the time he was the lieutenant of the Bologna National Guard, captured by the Austrian Hussars who had deposed the Bazzano municipality. A souvenir of this event is the so-called "Foscolo cell" on the ground floor of the fortress, to the right of the loggia.
During the 19th century a theatre was set up in the "Giants' Room" and in 1873 the "Arsenio Crespellani" Civic Museum was founded, created by Arsenio Crespellani and some Bazzano citizens following the discovery of the storage pit which holds archaeological artefacts from the area dating from pre-history to the Renaissance. There are also other rooms for educational activities, an audiovisual library and the areas reserved for conventions and cultural events.