After the assassination of Pier Luigi Farnese, Duke of Parma, son of Pope Paul III, the papal states wished to regain the duchy he had set up.
Despite assistance from French troops, Orazio Farnese, Ottavio's brother and the Duke of Castro, was beaten at Crevalcore, near Mirandola.
[1] Henry II also ordered Charles de Cossé, Count of Brissac to invade Piedmont, forcing Gonzaga to lessen his pressure on the duchy of Parma in September 1551, making it bear the main burden of the war.
In 1551 Julius sent his nephew Gian Battista Del Monte to besiege Mirandola, then held by a small French force under Piero Strozzi.
This mandated a two year truce, allowing Ottavio to make a peace treaty with the pope and restoring the duchy of Castro to the Farnese.