PARIS - The opening of Europe's financial markets tonight will unleash a battle that may decide the fate of the single currency and, with it, the cherished vision of European integration.

The 16 countries which share the euro will test an unprecedented strategy to defend their currency, pushed to the brink by the Greek debt crisis and relentless pressure from investors.

Approved at an emergency summit in Brussels, their war plan entails lending Greece €80 billion ($142 billion) over the next three years, supplemented by €30 billion from the International Monetary Fund.

It also sets up an arsenal - the European Stabilisation Mechanism - endowed with up to €70 billion - to defend the currency against speculative attack, a measure described by the zone's financial chief, Jean-Claude Juncker, as "a watertight line of defence."

And it aims to shore up confidence in the euro's management by hastening the reduction of budget deficits and punishing eurozone countries that breach guidelines on borrowing.

French President Nicolas Sarkozy spoke of a "general mobilisation" in support of the euro. "There is no doubt that the eurozone is going through the most serious crisis since its creation."

Before MPs approved Germany's contribution of more than a quarter of the European bailout, German Chancellor Angela Merkel said, "We are at a crossroads. What is at stake is no more or less than the future of Europe."

Greece got itself into the mess by going on a massive borrowing spree. At the end of 2009, the country of 10.7 million people had debts officially tallied at €273 billion, or 115 per cent of gross domestic product. Without help, it would default - essentially be declared bankrupt - when a tranche falls due on May 19.

Driving political action is fear of a domino effect that would topple similarly weak, highly indebted, uncompetitive economies, starting with Portugal, Spain, Ireland and Italy.

Panic over this contagion, and worries about violence in Athens in response to the Government's austerity package, drove stock markets around the world into a tailspin at the weekend and the euro to a 14-month low against the US dollar.

The Brussels summit declared that all EU institutions, including the European Central Bank, would use the "full range of means available to ensure the stability of the euro area".

"We will defend the euro whatever it takes," the president of the EU's executive commission, Jose Manuel Barroso, told a news conference.

A diplomat commented: "We have to smash the notion of inevitability, that we are somehow in Ten Little Indians," an Agatha Christie play about serial killings.

As the crisis has amplified, anger at rumour mongers and short sellers suspected of sabotaging the euro has risen.

"To some degree, this is a battle between politicians and the markets," Merkel said in a speech in Berlin.

Jean-Pierre Jouyet, the president of the Financial Markets Authority, said that he had asked the police and domestic intelligence service to intervene swiftly in tapping phones, intercepting emails and tracking internet traffic when suspected casesof market manipulation arose.

"These rumours have helped to impoverish entire populations. [They] endanger the security of European states."

Will it work? Will the markets calm down, frightened by the war chest, reassured by Greece's austerity plan and the action of the EU leadership?

"Nothing is less sure," commented Le Parisien. "The tardiness of the EU in getting its act together, the splits between countries, especially France and Germany, the weakness of economies that are still battered by the 2008 crash - it all points to pain in the coming days."

Long-stifled doubts are being voiced over the 1992 design of the euro, in which participants surrendered national currencies but not political sovereignty. That weakness enabled the Greeks to cook the books and let other countries recklessly expand their borrowings, say critics.

Thirteen of the 16 eurozone members have bust the budget guidelines.

"European Monetary Union was a political project imposed on unenthusiastic electorates by political leaders in a hurry," British Labour MP Gisela Stuart told Die Welt.

"However, it was based on very bad economics, and ultimately bad economics leads to bad politics, which we are beginning to see."