About 8,000 demonstrators chanted anti-austerity slogans and hoisted banners warning Angela Merkel she was not welcome in Greece at a protest on the eve of a visit by the German chancellor.
Organised by labour unions fed up with wage and benefit cuts during three years of austerity, the demonstration was called before Merkel announced she was coming to Greece in a gesture of support for the government's fiscal reform efforts.
But protesters did not miss the opportunity to vent their anger at Merkel, whose insistence on a tough reform programme many Greeks blame for their country's plight.
The main banner in front of parliament was a large German flag emblazoned with the words "Angela, you are not welcome!".
"We want Merkel to leave Greece alone because her measures only bring poverty," said protester Antigone Beza, 48, an Athens saleswoman. "We will fight and we will resist and we will shout 'Go home!'"
Greece is preparing extensive security measures for tomorrow's six-hour visit, Merkel's first to Greece since the debt crisis erupted there in 2009.
Police have banned gatherings in most of central Athens and will deploy 6,000 police as well as anti-terrorist units and rooftop snipers.
The German leader, who has been caricatured as a Nazi in the Greek press, has softened her rhetoric in recent months, apparently having decided that Greece should stay in the euro zone for now.
The Greek government is in negotiations with international lenders on more budget cuts to secure the vital next instalment of a €130-billion bailout keeping Athens afloat. The measures are sure to prompt more protests.