More than 300 million Europeans began swapping their old currencies for the euro at midnight Monday in the most ambitious currency changeover in history, one which the euro's architects hope will help realize dreams of a united Europe.

Citizens in a dozen countries were able to withdraw their first crisp new notes a decade after the euro was conceived with the Maastricht Treaty and three years after it began its virtual life underpinning the exchange rates of the mark, peseta, drachma, lira, franc and other national currencies that it replaces.

From Paris to Athens, Rome to Madrid, Europeans ushered in the euro with extravagant firework displays, live bands and huge parties in public squares. Outside of the European Central Bank headquarters in Frankfurt, officials lit a huge blue euro symbol.

Finland and Greece, on the currency zone's northern and southern most fringes, led the 12 nations welcoming the euro as a symbol of economic stability, with the New Year's arrival an hour before the rest of the continent and two hours before Ireland.

In Helsinki, Finnish Finance Minister Sauli Niinisto made the first official purchase: a cup of coffee for with a euro coin, worth 88 cents, at the Casino Ray.

And in Athens, Greek Premier Costas Simitis withdrew euro bank notes from an automatic teller machine, which he deposited in a charity box for UNICEF. Minutes later, hundreds of people flocked to ATMs.

"This is a milestone in Greek history. Now we are part of united Europe," Simitis said.

Though the euro is central to continental Europe's vision of tighter political union, it first became legal tender at midnight (3 p.m. EST) on tiny Reunion Island, a French department in the Indian Ocean.

More than 15 billion notes and 52 billion coins — worth 646 billion euros, or $568 billion — have been produced for the switchover. Six billion notes and 37.5 billion coins already are in banks and stores, the front lines in what has been the world's largest peacetime logistics operation.

Though it has lost 25 percent of its peak value against the dollar, the euro has generally been viewed as a success — eliminating fluctuations in national currencies, encouraging cross-border trade and pushing countries to budget carefully and liberalize their economies.

The 12-nation euro zone represents one-sixth of the world's economy, and is set to grow as the European Union expands eastward.

"I firmly believe that, because of what the euro has shown it can achieve, and also because of the shared values it symbolizes, Europe is stronger than it would ever have been without the dream of the euro coming true," European Central Bank President Wim Duisenburg said in Frankfurt on Monday.

Europeans for the last time used their old familiar money exclusively to ride the train and shop on Monday, before the new euro banknotes first become available at many of the euro zone's 200,000 automatic teller machines.

In anticipation, banks across the euro zone disabled ATMs in the afternoon, switching software and loading them with euro notes to dispense to eager consumers at the stroke of midnight. Three countries — Austria, Luxembourg and the Netherlands — expect all ATMs to distribute euros on New Year's Day, with others pledging to follow within days.

Still, there were lines across Europe as people filled their wallets one last time with outgoing notes — from Europe's oldest, the drachma, dating back 2,650 years, to the continent's most powerful, the German mark.

Italians were stocking up on the lira, withdrawing some 1.2 trillion ($550 million) on Saturday, more than double the amount on the same day last year, according to the Italian Banking Association.

Confusion emerged in Lisbon, Portugal, where signs adorning the 2,000 parking meters notified baffled drivers with only escudos in their pockets that they would accept only euros. The switch actually took effect at midnight.

As the euro countdown wore on, the mood was one of nostalgia as much as anticipation, with newspapers filled with tributes to their soon-obsolete bills and coins.

Spain's El Pais bid farewell to the peseta, calling it the "old companion." France's Liberation ran a short obituary to the 700-year-old franc: "The franc is dead [2002]."

European leaders adopted the euro over the skepticism of many citizens reluctant to relinquish symbols of national sovereignty. Only France and Denmark held referendums on adopting the euro — and the Danes voted to sit out the historic project along with Sweden and Britain, the three European Union holdouts.

Acknowledging the public's attachment to national currencies, architects of the euro expressed hope it will become a potent symbol of European unity.

"A vision is becoming reality," Helmut Kohl, the former German chancellor who with the late French leader Francois Mitterrand championed the single currency, wrote in the conservative Frankfurter Allgemeine Zeitung on Monday.

"It means there is no turning back from the path toward unification of our continent."

Dutch newspapers echoed his sentiments, and said building a stronger Europe shouldn't stop with the euro. The Volkskrant insisted that the new currency constitutes "an important push" toward political union.

The euro's arrival secured, even the most staid allowed themselves a sentimental moment.

German Finance Minister Hans Eichel said he would keep a German mark coin "to remind me of the day. Maybe I'll put it with a euro coin."

"Together they stand for a development that seemed completely impossible 50 years ago," he wrote in the Berliner Morgenpost. "We had a good time with the mark, but saying goodbye to it doesn't sadden me."

The nations adopting the euro are: Austria, Belgium, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain. Those staying out are Britain, Sweden and Denmark.