The Visconti Castle of Trezzo was a mediaeval castle built between 1370 and 1377 by Bernabò Visconti, Lord of Milan, at Trezzo sull'Adda, Lombardy, Northern Italy. 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.

Bernabò or Barnabò Visconti was an Italian soldier and statesman who was Lord of Milan. Along with his brothers Matteo and Galeazzo II, he inherited the lordship of Milan from his uncle Giovanni. Later in 1355, he and Galeazzo II were rumoured to have murdered their brother Matteo since he endangered the regime. When Galeazzo II died, he shared Milan's lordship with his nephew Gian Galeazzo. Bernabò was a ruthless despot toward his subjects and did not hesitate to face emperors and popes, including Pope Urban V. The conflict with the Church caused him several excommunications. On 6 May 1385, his nephew Gian Galeazzo deposed him. Imprisoned in his castle, Trezzo sull'Adda, he died a few months later, presumably from poisoning.