But the mood inside the cordon remained mostly good-humored with a jazz band, drummers and street theatre groups keeping the crowds entertained throughout the afternoon.

CNN: Protesters voice dissent on eve of G-20

Groups of masqueraded dancers, actors, singers and instrumentalists delight crowds with theatrical and musical performances based on historical as well as current events.

UNESCO: Intangible Cultural Heritage

Among the crowds are groups of pilgrims, who've traveled to Rome for the special and emotional occasion, as well as local residents and curious visitors keen to share in the moment.

CNN: STORY HIGHLIGHTS

The force said people should report suspicious activity such as large groups of people gathering, park their cars in well-lit areas or garages, avoid crowds and keep rubbish bins out of sight.

BBC: Kent teenagers held on 'social network riot incitement'