Greek public sector workers, who are bearing the brunt of wage and pension cuts as part of Greece's austerity programme, have begun a 48-hour strike.
Their action comes ahead of a nationwide general strike on Wednesday.
The programme has been introduced in return for a 110bn euro (£95bn) world rescue package agreed for the country.
Some protesters breached security at Greek landmark the Acropolis, and unfurled banners.
Sally Eden reports.