The rally was organised without the involvement of trade unions, political parties and other organisations, rather it relied heavily on ordinary citizens, or "netizens", who learned about it from social media such as Facebook, Twitter and others.
A Facebook site set up by 'Aganaktismenoi sto Syntagma' ("Indignant at Syntagma"), a reference to the eponymous square in front of the Greek Parliament, had garnered more than 33,000 'likes' by the time the demonstration started at 6 p.m. (16.00 GMT).
Thousands, mostly young people flooded the city's main square, peacefully demonstrating their indignation at the austerity measures announced by the government, and, in general, over the ongoing economic and fiscal crisis in the country.
A similar initiative took place in other cities across Greece, with mostly young people in the northern city of Thessaloniki holding a peaceful rally in front of the White Tower on the city's seafront.
Organisers warned that the mobilisation would be peaceful and without banners or placards indicating whatever organised collective identity. They also warned that they will not accept "party participations and interventions."
Thousands of demonstrators also occupied the seafront boulevard in the early evening, holding a sit-down protest.