On the twelfth day of unrest since a police officer's fatal shooting of a schoolboy triggered riots and arson, protesters unfurled two large pink banners from the stone walls of the ancient hilltop citadel, which looms over Athens.
"Thursday 18/12 demonstrations in all Europe," one banner read in Greek, English, Italian and German, while the other simply bore the word: "Resistance".
"We chose this monument to democracy, this global monument, to proclaim our resistance to state violence and demand rights in education and work," said one protester, who declined to give his name. "(We did it) to send a message globally and to all Europe."
A government spokesman, Evanguelos Antonaros, said the protests were "inexcusable" and accused the protesters of tarnishing Greece's image abroad.
The riots, which caused millions of pounds' worth of damage in Athens and a dozen other Greek cities, were fuelled by intense anger and frustration among young Greeks over low wages, high unemployment, police brutality and government corruption.
They have already inspired sympathy protests in cities across Europe, from Spain and France to Italy and Turkey. European leaders, including French President Nicolas Sarkozy, have expressed concern that they might spread as the global financial crisis worsens unemployment and economic hardship.
Nearly two weeks after the Dec 6 shooting of 15-year-old Alexandros Grigoropoulos in the edgy, graffiti-plastered Athens district of Exarchia, the anger of the protest movement shows no signs of abating.
In the latest violence, a gang of youths threw petrol bombs at a riot police bus in central Athens. The driver managed to escape unharmed but the vehicle was damaged, police said.