Earlier in the day, 27 EU leaders, not including the United Kingdom, have signed a declaration to honor the 1957 Rome treaty, which led to the the foundation of the bloc.
According to the Rainews24 broadcaster, police detained 122 people for identification in order to manage the risks of disorder at the protests.
Around 25,000 protesters are expected to participate in six separate protests — both pro- and anti-Europe — that are being held in the Italian capital throughout the day.