BERLIN - Germany on Monday celebrated the anniversary of its reunification 21 years ago, which put it at the heart of an increasingly united Europe now being tested by the eurozone debt crisis.

Chancellor Angela Merkel, President Christian Wulff and others gathered at what was once the parliament building in the former West German capital, Bonn, for a ceremony marking the anniversary.

West Germany and communist East Germany were united on Oct. 3, 1990, less than 11 months after the east opened the Berlin Wall.

The identity of West Germany, and later of the reunited Germany, "has been closely linked from the beginning with the commitment to Europe," supreme court chief justice Andreas Vosskuhle told the country's leaders.

Germany has the European Union's biggest economy and is a key player in trying to stem the debt crisis, though rescues of debt-laden eurozone strugglers are unpopular at home.

Vosskuhle said that European institutions "must not immunize themselves against criticism from their citizens," and that "where Europe is going must not be decided in elite circles alone."

"At the same time, we must always make clear that Europe cannot be reduced to a simple mathematical calculation," he said. He added that the EU is based on the recognition that long-term peace and prosperity can only be secured by a close union -- and "that goes for good as well as bad times."

Vosskuhle's Federal constitutional Court has had a part in the debt drama, recently upholding Germany's participation in bailouts but stipulating that lawmakers must have more of a say on future rescue measures.

Bonn hosted this year's ceremony because North Rhine-Westphalia state, where it is located, holds the rotating presidency of the German parliament's upper house.