Castle of Trezzo sull’Adda: A Medieval Fortress and Visconti Stronghold
Site at a Glance
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- Italy
- Primary era
- Medieval
- External website
- Open
- Eras represented
- Medieval
- Civilizations
- Holy Roman Empire, Lombard
- Site type
- Military
- Remains
- Castle
On this page14 sections
History
The Castle of Trezzo sull’Adda is a medieval fortress in Trezzo sull’Adda, Italy, built on a hill or peninsula at a bend of the Adda River. The river protected two sides of the site, while fortifications closed the landward side and controlled an important crossing. Celtic communities inhabited the area in prehistoric times, and Lombard communities occupied it after the seventh century, establishing the first known fortifications.
Early Fortifications and Imperial Conflict
The defensive works were altered repeatedly from the early Middle Ages through the thirteenth century. Earlier elements included the Teodolinda Tower at the northern end of the peninsula and the Black Tower on the eastern side. Tradition associated the Black Tower with Frederick Barbarossa, the twelfth-century Holy Roman Emperor whose conflicts with Milan shaped the early history of the fortress.
Barbarossa took possession of Trezzo in 1158 and ordered an expansion that strengthened the site and added towers. After he was expelled, the Milanese dismantled these fortifications. This earlier fortress is also broadly dated to around 1160, reflecting the rebuilding and alteration that followed the struggle between the emperor and Milan.
The Visconti Castle
By the late thirteenth century, the Visconti, the ruling family of Milan, had extended their territories across northern Italy. When Galeazzo II and Bernabò Visconti divided the family’s dominions after 1355, Trezzo became part of Bernabò’s eastern territory.
In 1370, Bernabò ordered a new castle to be built over the earlier fortress as part of a wider program of territorial defense. Completed in 1377, the complex served first as a residence and hunting retreat. It was later converted into a prison, giving the fortress a more confined and punitive role within Bernabò’s domains.
In 1385, Gian Galeazzo Visconti, the son of Galeazzo II and Bernabò’s nephew, staged a coup, arrested his uncle, and seized control of the Visconti territories. Bernabò was confined at Trezzo and died in his cell a few months later, reportedly after being poisoned.
Captures and the Siege of 1416
The death of Gian Galeazzo in 1402 produced a crisis that fragmented the Visconti state. Paolo Colleoni, father of Bartolomeo Colleoni, occupied the castle, and Paolo with his relatives captured it on 23 October 1404. They used Trezzo as a base for raids into the surrounding territory.
Pandolfo Malatesta later attempted to seize the fortress. During a revolt by prisoners inside, Paolo Colleoni, his brother Pietro, and their cousin Giovanni climbed the walls and occupied it. A more romantic tradition claims that they entered disguised as wine sellers. Paolo was apparently killed by his relatives while playing checkers, and his wife Riccadonna was imprisoned.
In 1416, Filippo Maria Visconti, Gian Galeazzo’s successor, instructed Francesco Bussone da Carmagnola, a professional military commander serving an Italian state, to retake Trezzo. Carmagnola besieged the castle from the west. Supplies continued to arrive from the east across the bridge, so he undermined one of its abutments and caused the bridge to collapse.
Decline and Conservation
After the 1797 Treaty of Campo Formio ended the political boundary between Milan and Venice along the Adda, the castle lost much of its strategic importance. During the eighteenth and nineteenth centuries, sections of its walls were dismantled for building material. Nineteenth-century quarrying near the river destroyed the older Black Tower. Decorative elements were transferred to the Royal Villa of Monza, while stone from the collapsed bridge was carried to Milan for the construction of the Napoleonic Arena, also known as the Arena Civica.
The municipality acquired the castle, and restoration of the ruins began at the end of the twentieth century. The surviving tower and eastern casemates were incorporated into the restored use of the remains. In the early twentieth century, the Taccani hydroelectric power plant was built at the foot of the hill, with its architecture designed in consideration of the castle’s proximity. The ruins, the power plant, and the Adda’s natural environment now form the historical landscape of Trezzo.
Remains
The surviving castle occupies the southern part of the Trezzo peninsula, where the Adda forms its principal natural defense. The earlier northern fortifications were not substantially altered by the Visconti rebuilding. The later complex combined a long central building, a high tower, walls, underground fortified chambers, and a bridge across the river. Much of the castle is ruined, while the surviving tower and casemates remain in good condition.
Castle Structures
Central Building and Tower
The central building had an elongated rectangular plan running from south to north. A square tower, 42 meters high, stood a few meters south of it and was linked to the building by two walls. Together with the other defenses, these elements formed a roughly pentagonal plan. The castle was built with stone, river cobbles, and brick. Its masonry mainly used river pebbles separated by brick courses, while ashlar blocks were concentrated in the southern walls and the tower, whose stonework was rusticated.
Casemates
Casemates, fortified chambers used for protected movement, storage, or military activity, were constructed beneath the walls along the two sides parallel to the Adda. Some were cut directly into the rock. The surviving casemates are on the eastern side of the castle and form one of the principal preserved parts of the defensive system.
Fortified Bridge and Older Towers
Bridge Abutments
The fortified bridge crossed the Adda on a single arch measuring 72 meters in span, 8 meters in width, and 25 meters above the water. Towers at both ends controlled passage, while a lower internal walkway separated pedestrians from carts. The bridge connected the castle with Bernabò Visconti’s eastern territories. Its destruction during Carmagnola’s 1416 siege followed the undermining of one abutment, and the surviving abutments remain associated with the castle.
Teodolinda Tower
The older Teodolinda Tower stands at the extreme northern end of the peninsula and is visible from the riverbank. It belonged to the earlier defensive arrangements that preceded the principal Visconti castle.
Black Tower
The Black Tower formerly stood on the eastern side of the peninsula and was traditionally linked with Frederick Barbarossa. It was destroyed during nineteenth-century quarrying near the Adda, leaving the later castle remains, the northern tower, and the bridge abutments as the principal surviving elements of the site.
River Setting and Later Industrial Structure
The Adda encloses or protects two sides of the promontory and explains the castle’s defensive position at the river crossing. The Taccani hydroelectric power plant stands at the foot of the hill. Its early twentieth-century architecture was designed with regard to the nearby castle, and the plant remains part of the area’s present river landscape.
