Overshadowed by the power of the nearby Alessandria, it attracted the attentions of Galeazzo I Visconti, duke of Milan, but his plot to capture the city failed.
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In 1635, during the Thirty Years' War, Valenza resisted for 6 days a siege from French, Parmense and Savoyard troops.
The section from Casale Monferrato to Valenza was opened on 22 March 1857 as part of the railway from Vercelli to Valenza.
Scavia in Castellazzo Bormida (Province of Alessandria), and that of Signor Vaccari in Valenza, and of the Soldiers Fallen in Africa erected in the town of Valenza.