European Union (EU) leaders gathered in Lisbon on Tuesday evening to celebrate the entry into force of the Treaty of Lisbon, ending an eight-year horse-trading and setbacks in the course of the bloc's institutional construction.

Leaders of the three major EU institutions -- the Council, the Commission and the Parliament -- attended a two-hour ceremony at a specially built temporary venue next to the River Tagus, near where the treaty was signed on Dec. 13, 2007.

"Today EU citizens are heading into a new era," said Swedish Prime Minister Fredrik Reinfeldt, whose country is still holding the out-going rotating EU presidency until the end of this month.

"Today is the first day for a more efficient, more modern and more democratic EU, for all citizens," he spoke to several hundred guests.

He said it was "not an easy journey" since the signing of the treaty two years ago till its entry into force. "It took a lot of efforts," he noted.

The coming into force of the treaty was not only important for the EU, but also for the whole world, Reinfeldt said, as the EU's "inward-looking comes to an end" and shifted to "outward-looking" and the bloc was well prepared to address the financial and economic crisis.

The EU would then focus its attention and effort on challenges such as climate change and promotion of scientific research and innovation.

"The Lisbon Treaty is ... the symbol of a reunited, free and democratic Europe," said European Commission President Jose Manuel Barroso, who also warned the treaty was not an end in itself.

"Nothing can replace leadership, determination and political will," he added.

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.

The treaty is a simplified version of a constitution treaty that was approved by EU leaders in 2004 and but aborted due to French and Dutch voters' rejection in 2005.

Herman Van Rompuy, who will become the first European Council president on Jan. 1, echoed Reinfeldt at the ceremony that the treaty had "a long and stormy journey."

At the same time he described the treaty as "a powerful tool with which (we) tackle the challenges of our time," saying, "It will allow us to play our part on the world stage."

The treaty should have been put into force in January 2009, but it was postponed as Irish voters rejected it in June 2008 during the ratification process in member states.

Under the treaty, the European Parliament and national parliaments will have a much greater say in the EU's decision-making process and European citizens will be given the opportunity to influence proposed EU laws.

To give more rights to EU citizens, the charter of fundamental rights will be given the same legal status as the EU treaties themselves.

Through effective and streamlined institutions, including swifter, more consistent decision-making on law and order issues, the EU will have greater ability to combat crime, terrorism and human trafficking.

The creation of new posts will bring more coherence between different strands of its external policy and give the Union the capacity to deliver change and to open up their opportunities to shape globalization.

Aside from Van Rompuy, who was elected on Nov. 19 the first president of the European Council, Britain's Catherine Ashton, incumbent EC Trade Commissioner, was chosen as the high representative of foreign and security policy, or foreign minister.