The vandalism of more than 40 graves of German soldiers killed during World War I came on the eve of the highly symbolic meeting in Reims in northern France, a region scarred by centuries of war with Germany.
French President Francois Hollande moved quickly to limit the damage.
"No dark force and even less stupidity can alter the deep Franco-German friendship," he told German Chancellor Angela Merkel and others gathered in the cathedral at Reims.
"Our friendship inspires Europe," he said. "We don't want to preach. We just want to give examples to be followed.
"Madam Chancellor, I propose from our side to open and even cross a new door together that will lead to even closer friendship between our two nations."
The two leaders reviewed troops from their countries, exchanged kisses on the cheeks in greeting, and called each other "dear" Angela and Francois in stark contrast to earlier more formal, and even frosty, meetings.
The main event at Reims cathedral, a UNESCO world heritage site extensively damaged by German bombing during World War I, was attended by a hundreds-strong cheering crowd.
Merkel's message was more direct.
"Europe is more than just a currency, and the Franco-German relationship is vital in this regard, it has deeply marked European unification," she said.
At the same time she stressed that others were welcome to join in, echoing Hollande who is seeking closer ties with Italy and Spain.
“We must now put finishing touches on a political level of the economic and monetary union, it's a Herculean task but Europe is up to it," she said, ending her speech with "Long live Franco-German friendship" in both languages.
They also unveiled a plaque in German commemorating the "Mass for peace" before visiting an exhibition in the nearby Tau Palace.
Hollande, speaking to reporters after the ceremony, rejected the need for a super "Mr Euro" with beefed up powers, saying: "We are mobilised to preserve, nurture and strengthen the euro.
"We will have a good solution once Mr Juncker ends his mandate, a Franco-German solution," he said, referring to Luxembourg Prime Minister Jean-Claude Juncker who has steered the Eurogroup since 2005, whose term ends on July 17.
The Franco-German post-war reconciliation was symbolically achieved in 1962 by then French president Charles de Gaulle and German chancellor Konrad Adenauer.
The eurozone's two top economies have worked closely in recent years to try to solve the debt crisis hammering the single currency. Eurozone finance ministers will meet Monday in Brussels to build on measures agreed last month to tame the debt crisis.
Observers are watching to see how the relationship develops between the new French president, a centre-left advocate of growth, and Merkel, a centre-right defender of austerity.
The two have already locked horns on resolving the crisis. Hollande has pushed for more spending to boost growth -- a position winning over more adherents in Europe - while Merkel advocates serious belt-tightening and more fiscal control.
Hollande told reporters that the relationship was developing well. "Even though we belong to different political traditions, Mrs Merkel and I share the same values with regard to the EU," he said. "Our relations are good and there's no need to try to too hard."
They had always had a frank relationship, he added: "We say things, try to find compromises, without being emotional while at the same time conscious of our responsibilities."
On the eve of the their meeting, the graves of dozens of World War I German soldiers were found desecrated at a military cemetery some 40 kilometres east of Reims.
The local prefecture said the wooden crosses had been kicked over, broken and in some cases burned at Saint-Etienne-a-Arnes cemetery, which hosts the graves of some 12,000 World War I soldiers - most of them German.
Beer bottles were found scattered around the site and there was no sign of any political message.
Reims was occupied by the Prussians in 1870 and devastated by bombing during World War I.
It was here where on May 7, 1945, US general Dwight D. Eisenhower and the Allies received the unconditional surrender of the German Wehrmacht.