It included a massive tower, 42-meter high, and a fortified bridge on the Adda river on a single arch with a record 72-meter span.

[2] Since prehistoric times, the castle's site hosted a Celtic settlement and, after the 7th century, was inhabited by Lombard populations.

[5] In 1370, Bernabò ordered the construction of a new castle on the Trezzo peninsula, as part of a broader plan to fortify the territories under his rule.

Along the two sides of the castle, parallel to the river's course, casemates were built under the wall, partly excavating the rock.

[6] Bernabò's project included a fortified bridge over the Adda river that connected the castle to the eastern territories under his rule.

[10] Paolo Colleoni, the father of Bartolomeo and member of a family from Bergamo longtime opposer of the Visconti, occupied the Trezzo castle.

In 1416 Filippo Maria Visconti, son and successor of Gian Galeazzo, instructed the condottiero Francesco Bussone da Carmagnola to retake Trezzo.

After the unification of the territories of Milan and Venice, laid down in the Treaty of Campo Formio in 1797, the Adda river no longer marked their border.

Being Trezzo in the proximity of the inlet of the Martesana Canal, the blocks of the collapsed bridge were easily moved to Milan, where they were used in the construction of the Napoleonic Arena Civica.

The restored ruins of the castle, the Taccani hydroelectric power plant, and the Adda river's natural environment characterize today the Trezzo area.