Leaders of the European Union (EU) signed a declaration on Sunday on the occasion of the 50th birthday of the union, vowing to achieve "a renewed common basis" by 2009.
The document was signed by German Chancellor Angela Merkel, Jose Manuel Barroso and Hans-Gert Pottering, representing the EU presidency, the European Commission and the European Parliament respectively.
"We are united in our aim of placing the European Union on a renewed common basis before the European Parliament elections in 2009," the document reads.
Merkel said the EU members need to work even more closely to overcome the current and future challenges, including terrorism, climate change and illegal immigration.
Speaking at an official ceremony that marks the 50th anniversary of the Treaties of Rome, Merkel said the 27-nation union needs reforms to remain strong and competitive.
"On its own, every European country is too weak to successfully tackle the global challenges we face. That is why there can only be one answer: we must not act alone but together in a united Europe," said Merkel.
She warned that the unification of Europe cannot be taken for granted. "Whether or not on March 25, 2057 the centenary of the Treaties of Rome will be celebrated in a Europe of peace and freedom, democracy and the rule of law, we do not know."
She said Europe needs to remain dynamic in the context of globalization because other regions in the world are developing at a breathtaking pace.
Barroso, in his speech, called for unity and political will from leaders of member states.
"My vision of Europe is not one where only European institutions promote unity and member states defend diversity," said Barroso.
"A real partnership is where European institutions respect diversity and national governments promote unity," he added.
He told the 27 heads of state and government: "It is tempting, but it is not honest for national politicians to take all the credit and give Brussels (EU institutions) all the blame. Let us resist that temptation. This is the ethic of European responsibility that we must all share."
He asked the national leaders to give the EU institutions the capacity to act.
Pottering, for his part, urged the EU members to "put people in the center of the EU," calling for a more open democracy and citizen-oriented principles.
"We also know that we must continue our efforts to make the European Union more democratic, more open and closer to its citizens."
The Berlin Declaration, setting out EU values and future goals, falls short of mentioning the word "constitution."
The EU constitution, designed to streamline EU regulations and raise its efficiency, is virtually dead after two of the EU founding members -- France and the Netherlands -- rejected the draft text in separate referendums in 2005.
Merkel, expected to present a roadmap for the revival of the constitution by the end of Germany's EU presidency in June, had hoped for a strong push for the constitution during the summit in Berlin.
The ambitious plan has recently been played down due to the disagreements among the 27 EU members.