Dozens of people have been hurt and some 350 people arrested as anti-austerity demonstrators clashed with police in the German city of Frankfurt.
Police cars were set alight and stones were thrown in a protest against the opening of a new base for the European Central Bank (ECB).
Violence broke out close to the city's Alte Oper concert hall hours before the building's official opening.
Thousands of "Blockupy" activists were due to take part in a rally.
Organisers were bringing a left-wing alliance of protesters from across Germany and the rest of Europe to voice their anger at the ECB's role in austerity measures in EU member states, most recently Greece.
Police set up a cordon of barbed wire outside the bank's new 185m (600ft) double-tower skyscraper, next to the River Main.
But hopes of a peaceful rally were dashed as clashes began early on Wednesday.
Tyres and rubbish bins were set alight and police responded with water cannon as firefighters complained they were unable to get to the fires to put them out.
Police spokeswoman Claudia Rogalski spoke of an "aggressive atmosphere".
The ECB's new headquarters cost an estimated €1.3bn (£930m; $1.4bn) to build and is the new home for thousands of central bankers.