In 1450 Francesco I Sforza was backed by the family in his struggle to become heir and successor of the Visconti dukes and used the castle as a base for his siege of Milan. When he became duke, his gratitude for the family's services overwhelmed them with rewards and honors, among which was the title of a count of Peschiera  for Vitaliano's son Filippo Borromeo (1419–1464) in 1461.
In 1450, Francesco I Sforza was backed by the family to become heir and successor to the Visconti dukes, using the castle as a base for his siege of Milan. After becoming duke, he rewarded the family with honors including the title of count of Peschiera for Vitaliano's son Filippo Borromeo in 1461.