In 1848 Maestri participated in the March insurrection, joining up with his friend Bertani to organise an improvised ambulance service. The expulsion of the Austrian troops meant an end to censorship and unleashed a proliferation of leaflets, pamphlets and newspapers. Maestri teamed up with Romolo Griffini to launch "Voce del popolo" ("Voice of the people"), a daily tabloid-sized newspaper published in Milan between 26 March and 29 July 1848, with a cover price of . The newspaper was unusual, even among democratic-republican publications of the time, in the extent to which it demonstrated a concern with social problems. The "Voce" was aimed at a mass audience but represented an interesting experiment in Lombard journalism, and a test of the skills of its two young editorial-controllers. It was, of course, unflinching in its backing for republicanism and democracy, but it was nevertheless non-confrontational in its attitude to the provisional government in Milan, accepting that the detailed nature of future political institutions could only be determined once the war was over, but without yielding in its "people's war" supportive attitude to the national guard, constitutional principles and universal suffrage. The relatively conciliatory spirit in respect of moderate-liberal opinion was summed up in a strikingly "constructive mission statement" printed and signed by the two editors on 26 March 1848: "Our political approach, for now, is to be helpful, supportive and obedient to the provisional government" ("Il nostro motto politico è, per ora, aiuto, soccorso, obbedienza al Governo provvisorio"). At least one source reports that Maestri fought valiantly as an insurrectionist. After Field Marshal Radesky returned with a much larger army and reimposed Austrian control Pietro Maestri was imprisoned in the Castello Sforzesco, the large fortress in the city centre from where, traditionally, the city was garrisoned . He nevertheless escaped death.