People packed into Piazza San Giovanni, singing the anti-fascist anthem Bella Ciao, a staple of the movement’s demonstrations.
One of the movement’s founders, 32-year-old Mattia Santori, told the crowd the idea was to “bring out a new energy through a much freer and more spontaneous form” than a traditional political party “that will not be hierarchical” but would instead set “broad directions”.
One demonstrator held up a giant sardine model, while others carried drawings and posters.
The Sardines Movement was launched in Bologna just last month, when Santori and three friends invited people to protest against the League, whose popularity is rising ahead of an election in the northern region of Emilia-Romagna.
Since then, they have staged a series of rallies drawing tens of thousands in Milan, Florence, Naples and Palermo.
In late October, the League won a historic victory in regional polls in central Umbria, which had been led by the left for half a century.
Salvini is now campaigning hard to try to capture Emilia-Romagna, another left-wing stronghold.
With the election set for January 26, the polls suggest the League’s candidates are running neck and neck with the current centre-left governor.
Salvini has said he wants to conquer the regions one by one to bring down the current coalition between the Five Star Movement (M5S) and the centre-left Democratic Party (PD), and thus force early elections.
The ruling M5S was born out of a street protest in Bologna in 2007.
It triumphed in last year’s national election but support has dropped sharply since it forged a coalition first with the League, then the PD.
Founders of the Sardines Movement have said they do not intend for it to become a political party.
