European Union leaders have signed the European Union Constitution in Rome.
The document is designed to make the running of a 25-member Union more efficient and enable it to have more impact globally.
The constitution distills all previous EU treaties into a single charter, but it will not come into force until the parliaments of all member states have ratified it. If any member state rejects the document, it might never take effect.
The Taoiseach, Mr Ahern, who won plaudits throughout the EU for negotiating the final details of the constitution earlier this year told the signing ceremony today member states must ratify the historic accord quickly.
"It is of fundamental importance that all twenty-five Member States now ratify the European Constitution convincingly and on time. The process of ratification will not be easy, but, with energy and determination, it can and will be successful," he told EU leaders.
Mr Ahern added that today was an occasion for celebration.
"It is also an occasion for a fresh commitment to Europeans working together to ensure that the 21st-century Europe is a beacon of stability, prosperity, peace and justice in 21st century world," Mr Ahern added.
Today's lavish ceremony was staged on the Capitoline Hill in the same Renaissance palace where the EU's six founding nations signed the original Treaty of Rome in March 1957 to set in motion the European process.
Speaking at the ceremony, the European Commission President Mr Romano Prodi warned: "The signing of the European Constitution does not mean we have crossed the finishing line. In the months ahead the governments of the Union's 25 member states will need to use their best endeavours to persuade their parliaments and citizens to ratify the new constitutional treaty.
"These decisions we cannot take for granted."
German Chancellor Mr Gerhard Schroeder dismissed talk of a crisis within the EU. "I wouldn't talk about a crisis, not yet, if in the next two weeks we find an agreement and I think we will, the problem will have been overcome," he said.
The British Foreign Secretary, Mr Jack Straw, said Britain would likely hold its referendum on an EU treaty in early 2006.
"It is likely to be in early 2006 for the simple reason that in the autumn of 2005 we have the presidency of the European Union and it would be practically almost impossible to combine both running the presidency with a referendum," Mr Straw said.