Sansepolcrismo was the movement led by Benito Mussolini that preceded Fascism. The Sansepolcrismo takes its name from the rally organized by Mussolini at Piazza San Sepolcro in Milan on March 23, 1919, where he proclaimed the principles of Fasci Italiani di Combattimento, and then published them in Il Popolo d'Italia, on June 6, 1919, the newspaper he co-founded in November 1914 after leaving Avanti!

On March 2, 1919, Il Popolo d'Italia published a statement that included the program for a meeting for March 23, 1919. Further mentions of the meeting were published on March 4 in Genoa by the Fascist War Veterans publications Italia Redenta ("Italy Redeemed") and Pensiero e Azione ("Thought and Action"). Word of the meeting was then spread among various veterans' associations spread throughout Italy. The statement was reiterated later March 9 in Il Popolo d'Italia: "On 23 March an 'anti-party' will be created, the Fighting Fascists, who will face against two dangers: the reaction of the right, and the destructiveness of the left."

On the evening of March 21, 1919, the Union Local of the Association of Traders and Merchants in Piazza San Sepolcro officially formed the Fascio di Combattimento di Milano ("Milan Fighting Fascists"). Participants were afterward regarded as the so-called Fascio primigenio ("primitive Fascists"). After the first meeting of the council, they included: Benito Mussolini, Ferruccio Vecchi, Enzo Ferrari, Michele Bianchi, Mario Giampaoli, Ferruccio Ferradini, and Carlo Meraviglia. It also decided that the gathering of March 23 would be chaired by Ferruccio Vecchi and that their Executive Secretary would be Michele Bianchi.

In the previous days, rumors circulated that accused the Red Guards of planning to prevent the gathering. The night before, supporters began to organize in Milan, almost all veterans of World War I, but the morning of March 23 was found to be quiet at Piazza San Sepolcro and confirmed by Carlo Meraviglia, who had arrived in advance specifically to review the situation.

The meeting of the March 23, originally intended to be held at Teatro Dal Verme, had lower participation than expected, and ultimately was held in the meeting room of the Industrial Alliance in Piazza San Sepolcro in Milan, an arrangement made possible by the Industrial Alliance President, the interventionist Cesare Goldmann, who had financed Il Popolo d'Italia and also took part in the meeting. The first to speak was Ferruccio Vecchi, acting as chairman, who opened the meeting, followed by Lt. Enzo Agnelli, who gave greetings from the Milan Fighting Fascists, founded just two days before.

The first policy declaration was made by Mussolini, who spoke broadly on three fundamental points of the new movement. These were summarized on the following day in Il Popolo d'Italia:

I. This assembly of 23 March turns its first salute and its memory and reverent thought of the sons of Italy that have fallen to secure the greatness of the Fatherland and the freedom of the World, to the wounded and invalids, to all the combatants, the former prisoners who did their duty, and who declared themselves ready to energetically support the vindication of the material and moral order that was supported by the association of combatants [...]

II. This assembly of March 23 is opposed to imperialism at the expense of other peoples of Italy and Italian imperialism to the possible detriment of other peoples; it accepts the postulate of the Supreme League of Nations and the integration with regard to Italy must be realized in the Alps and the Adriatic with the claim and annexation of Fiume and Dalmatia. [...]
III. The Assembly of March 23, we the Fascists commit by all means to sabotage the neutralist candidates of all parties.