The initial settlement on Cidneo hill dates back to the Bronze Age, precisely to the 9th century BC. However, the first true building built there was a modest temple dedicated to the Celtic deity Bergimus. The most significant renewal of the hill was due to the Romans, who, at the end of the 1st century BC, integrated its perimeter within the city walls. During the same period, an imposing monumental temple was erected by the Romans that was supposed to have a nearly identical plan to that of the Visconti keep: the ancient supporting walls and the foundations of the staircase inside this area are still visible today.
Over the centuries and with the advent of Christianity, the area of Cidneo assumed an increasingly prominent role as a sacred place: a Paleochristian martyrium was built, later replaced by a large basilica, demolished in the 18th century following an explosion of a powder magazine, which caused serious damage to the monument. Today, only one of the two facade towers remains, known as the Mirabella Tower, which was presumably built on a Roman-era stair tower.
During the early Middle Ages, there is a progressive scarcity of information concerning the area under consideration. However, starting from the year 1000, such information begins to increase, although it is not possible to fully reconstruct the fortifications made during that period. In the period between 1237 and 1254, the city walls were expanded, giving Brescia the appearance that would characterize the city until the end of the 19th century. In this context, the area in question was characterized by the presence of numerous walls dating back to the Roman era, as well as a rich concentration of religious buildings, in addition to being the site of numerous markets and fairs.
During the Visconti domination period, important restructuring interventions of the city defenses were implemented. In particular, in 1337, the Cittadella Nova was built, a city wall that, starting from the castle, incorporated within it the ecclesiastical and civil power buildings of the city, namely the Broletto and Duomi areas, at that time consisting of the Old Cathedral and the Paleochristian basilica of San Pietro de Dom. The only testimony of this vast restructuring intervention that has come down to us is represented by the Mastio, intended to house the captain of the garrison, and characterized by rooms decorated with polychrome bands and geometric and floral motifs, of which only a part has been preserved.
In the same period, during the period of interest, a defensive system consisting of six towers, covered passages, and drawbridges around the Mastio was constructed. In addition, the Strada del Soccorso, which was later expanded in the sixteenth century, was traced to provide an escape route to the north, often used by enemies during the following centuries.
In 1426, the city of Brescia passed under the dominion of the Republic of Venice, which immediately set about restructuring the city fortifications, which had been heavily damaged during the war against the Milanese. These works were concluded in 1466 when the city walls were completely revised, lowered, and surrounded by earthworks and ditches. However, the castle underwent only marginal modifications, limited to the transformation of the towers from a square to a circular plan, of which only one tower on the northern perimeter has survived.
In 1509, the French army defeated the Venetian army and seized the city of Brescia and its castle. During the French domination period, new expansion and reinforcement works were started on the walls, but they were never completed. The San Martino monastery was demolished to make way for the walls that were supposed to be built in its place. It was during this period that Brescia went through its darkest period, as it was contested between the French masters and the Venetians who tried to regain it. The maritime republic managed to retake the city in 1512 but at a high cost in terms of human lives and sacrifices. The peak of the tragedy occurred on February 19th, when the city was sacked by soldiers from different political parties, including the French, who used the Strada del Soccorso to enter the fortress, the Gascons, the Germans, the Swiss, as well as the Cremonese and the Mantovans.
In the second half of the 16th century, with the return of the Venetians and the stabilization of the government, further improvements were undertaken to overcome the defects that emerged during the war, such as the expansion of the Strada del Soccorso previously mentioned. Following heated discussions about the feasibility of creating a new wall towards the front facing the city, also following tensions with Spain, which ruled the Duchy of Milan, in 1588 the project to build the bastioned walls was approved. The bastions of San Pietro, San Marco, San Faustino, and della Pusterla were then built. The fortress was also equipped with buildings for the storage of provisions, such as the Piccolo and Grande Miglio, as well as ovens, barracks, religious buildings, cisterns, and powder magazines. Following the shifting of the conflict line with Milan to the Adda and the consequent concentration of defensive efforts on Bergamo, the strategic function of the castle ends in this period, and history will never again involve it in any war-related activities, beginning a slow decline of the structure. Only the defense system was subsequently strengthened with many firing positions, but for a long time, the castle did not receive any relevant modernizations.
Under the new French domination, the castle did not undergo any improvement and was used as a prison and barracks. The same fate would have befallen it shortly after under Austrian domination. Nevertheless, Cidneo was still an excellent point of defense and attack. In 1849, during the ten-day uprising of Brescia, the population rebelled against the Austrian garrison following the refusal to pay for the lack of support to the Imperial Regio government during the First War of Independence. Unlike other cities, there were no previous open uprisings, only small disorders and requests for civic guards, assemblies, and formations of pro-independence groups led by Zanardelli but no revolt, and the troops’ removal from the city occurred peacefully, which is why the Brescians did not intend to pay. The soldiers barricaded themselves in the fortress and bombarded the city while waiting for reinforcements from Mantua. After ten days of fighting, the city was recaptured by Austro-Hungarian troops, thanks to the support brought by General Julius Jacob von Haynau, who entered the fortress using the Via del Soccorso.
After the war that led to the independence of Italy, which occurred in 1859, the Brescia castle ceased its military function to become a prison for military purposes. Following the acquisition of the hill by the municipality, a restoration work was undertaken that gradually transformed the fortress, denaturing its military purpose and leading it to the current state of entertainment center and venue for public events in Brescia.
Currently, the castle houses various institutions, including the Museum of the Risorgimento, the Luigi Marzoli Arms Museum which houses a collection of armor and weapons dating back to the medieval period, the Specola Cidnea, and two large miniature models of railways.