ROME (Reuters) - Europeans must contain their squabbling and carping about the EU if the Union is to survive, leaders warned on Saturday as they marked the 60th anniversary of its founding in Rome by signing a formal declaration of unity.

Four days before Prime Minister Theresa May, absent from the ceremony in the Italian capital, delivers an unprecedented blow to the bloc’s growth by filing Britain’s formal exit papers, her fellow leaders hailed 60 years of peace and prosperity and pledged to deepen a unity frayed by regional and global crises.

But days of wrangling about the wording of a 1,000-word Rome Declaration, May’s impending Brexit confirmation and tens of thousands of protesters gathering beyond the tight police cordon around the Campidoglio palace offered a more sober reminder of the challenges of holding the 27 nations to a common course.

“We have stopped in our tracks and this has caused a crisis of rejection by public opinion,” said their host, Italian Prime Minister Paolo Gentiloni, noting Britons’ repudiation of the EU.

He said the failure to push the project forward during a decade of economic slump had fuelled a re-emergence of “blinkered nationalism”. Rome offered a fresh start: “The Union is starting up again ... and has a vision for the next 10 years,” he said.

Others, however, are wary of such enthusiasm for giving up more national sovereignty -- and also of others in the Union moving faster with integration. Poland’s nationalist government has led protests against a “multispeed Europe”, which it fears would consign the poor ex-communist east to second-class status.

Leaders hailed the visionary “war generation” of leaders from old foes France and Germany who signed the Treaty of Rome in the same room on March 25, 1957, along with Italy, Belgium, Luxembourg and the Netherlands; some offered personal memories of their own generation’s debts to the expanding European Union.

Jean-Claude Juncker, the EU chief executive, recalled how his father in Luxembourg was forced into the German army in World War Two; Donald Tusk, the summit chair born in Gdansk a month after the Treaty was signed, remembered growing up in the ruins of war and yearning for freedom behind the Iron Curtain.

“That really was a two-speed Europe,” he said in a pointed dig at his domestic foes now ruling in Warsaw, who have tried to block a push by the western powers to deepen their integration.

German Chancellor Angela Merkel, the bloc’s dominant leader who faces a re-election test in September, stressed the Union must also address the complaints of generations for whom war is fading into history. “We will in the future have to concern ourselves above all with the issue of jobs,” she told reporters.

“UNITED, OR NOT AT ALL”

Fearing that the departure of its second-biggest economy and major global power could prompt the unravelling of the bloc, many leaders argue that only forward motion can revive popular support for the EU by generating economic and security benefits.

“Today we renew our vows and reaffirm our commitment to an undivided and indivisible Union,” Juncker told them, urging the bloc not to get bogged down in details that alienated voters.

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Tusk, too, warned against the impression the EU was about petty regulations: “Why should we lose our trust in the purpose of unity today? Is it only because it has become our reality? Or because we have become bored or tired of it?” he asked.

Merkel said leaders wanted to respond to people’s concerns, about the economy, welfare, migration and defence with “a protective Europe” that offered assurances on their wellbeing.

All 27 national leaders, along with the heads of Brussels institutions, signed a declaration which concluded: “We have united for the better. Europe is our common future.”

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They promised to listen to citizens. But locked away behind rings of armed police, the leaders may hear little of what thousands of protesters have to say on Saturday.

Addressing right-wing supporters of the Fratelli d’Italia movement, its leader Giorgia Meloni denounced a “great EU deception”. “The real enemies of Europe,” she said, “Are the bankers, usurers and technocrats.” The Union, she added, must be replaced by a new alliance of “free and sovereign countries”.

But for Maximilien De-Wyse, 26, from the northern French city of Lille, that was the wrong answer. Taking part in a pro-EU march in Rome, he recalled his Polish immigrant grandparents and said: “It is only united that we can save peace.”