The Battle of Castelfidardo was a battle of the Expedition of the Thousand that took place on 18 September 1860, at Castelfidardo, a small town in the Marche region of Italy. It was fought between the Sardinian army - acting as the driving force in the war for Italian unification, against the Papal States.On 7 September, Cavour, Prime Minister of Piedmont, sent an ultimatum to the Pope demanding that he dismiss his foreign troops.