Top European Union officials attended a ceremony Tuesday to mark the coming into force of the Lisbon Treaty, which is designed to ensure the bloc has a more influential say in world affairs.
The treaty took effect after years of wrangling within the 27-nation union over its provisions.
The glitzy ceremony took place at a specially built temporary venue next to the River Tagus, near where the treaty was signed two years ago. A logo of the treaty was projected onto a nearby 16th-century monument, and a fireworks display ended the hour-long ceremony for several hundred invited guests, including the prime ministers of Sweden and Spain.
European Commission President Jose Manuel Barroso said in a speech that the legal implementation of the treaty marked the completion of a 20-year cycle of European history since the 1989 fall of the Berlin Wall and the bloc's consequent expansion into Eastern Europe.
"The Lisbon Treaty is, in that sense, the symbol of a reunited, free and democratic Europe," he said.
However, he warned that the treaty was not an end in itself.
"Nothing can replace leadership, determination and political will," he said.
The treaty features new rules to accelerate decision-making so that the EU can respond more swiftly to global issues such as defense, energy security, climate change and migration.
Many Europeans expressed unease about the possibility the treaty might create a superstate that could neglect the concerns of individual countries.
The treaty is a revised version of a draft constitution that was approved by EU leaders in 2004 and was intended to mark a new era in European integration. But French and Dutch voters rejected it at the ballot box the following year.
EU leaders watered down the document and renamed it but then Ireland threw out the Lisbon Treaty in a referendum in June 2008 before reversing the decision in a second public vote two months ago.
Speaking at the ceremony, Belgium's Herman van Rompuy who becomes the first EU president on Jan. 1 said the agreement had "a long and stormy journey."
But he said the treaty was "a powerful tool with which to tackle the challenges of our time."
"It will allow us to play our part on the world stage," he added.