The rally commemorated the 1978 slaying of two members of a neo-fascist youth group in an attack later claimed by extreme-left militants.
Participants made a straight-armed salute that harks back to the fascist dictatorship of Benito Mussolini. Under postwar legislation, use of fascist symbolism, including the straight-armed gesture known as the Roman salute, is banned.
State TV channel Rai reported that Italian police were investigating the mass salute.
The rally was held on the anniversary of the slayings outside an office of what was the neo-fascist Italian Social Movement, a party formed after World War II that attracted nostalgists for Mussolini.
