France and Germany have marked the 100th anniversary of the World War One battle of Verdun in north-eastern France with a call for European unity.
France's Francois Hollande and Germany's Angela Merkel used Verdun as a symbol of both reconciliation between their nations and of EU integration.
Mr Hollande warned against "forces of division" in Europe. Mrs Merkel said nationalism "would throw us backwards".
The two stood side by side in memory of the 300,000 soldiers killed at Verdun.
The 10-months battle that began in February 1916 was the longest and one of the bloodiest in World War One. France eventually emerged victorious.
The main ceremony was held at the Douaumont Ossuary, which contains the bones of 130,000 German and French soldiers.
The French president and the German chancellor jointly lit a flame in the building.
Some 4,000 French and German children also took part in a re-enactment of a battle choreographed by German filmmaker Volker Schloendorff.
Addressing the children, Mrs Merkel said: "Hardly older than you was the French Lieutenant Alfred Joubert as he, 100 years ago, not far from here, lay in a trench. He confided to his diary: 'Not even hell could be this awful.'"
She went on to say that the EU proved its "ability to compromise to unite" and to condemn "pure nationalist state thinking and behaviour [that] would throw us backwards."
President Hollande said: "The forces of division, of closure and withdrawal are at work again. They cultivate fear and instil hatred."
He said France and Germany had a special responsibility to "end conflicts at our doorstep" and to "welcome the people who flee tragedy and massacre.
"Europe is capable of overcoming the greatest difficulties if it shows solidarity and responsibility", he said, citing the eurozone crisis as an example.
The ceremonies started early on Sunday, with the two leaders visiting the military cemetery at Consenvoye, north of Verdun, where 11,000 German soldiers are buried.
At Verdun city hall, Mr Hollande focused on Franco-German relations, saying that Mrs Merkel's presence showed that Verdun was not a symbol of suffering but one of hope.
In her speech there, Mrs Merkel said: "Only those who know the past can draw lessons and build a good future."
Remembering the famous 1984 image of former leaders Francois Mitterrand and Helmut Kohl holding hands at Verdun, she said: "We have reconciled and reached agreement; we have become friends."
The battle of Verdun, 21 February - 15 December 1916
- Verdun - a strong point on the long front line dividing the French and German armies - was the longest battle of World War One
- At the end of the bloodshed in December 1916, France won back nearly all the territory it had lost in February
- General Erich von Falkenhayn, the Chief of the General Staff and Germany's principal strategist, targeted Verdun because of its position on the Allied line and its sentimental value to French people
- Falkenhayn hoped to combine the Verdun offensive with a U-boat offensive against British shipping - the two campaigns together were designed to force France and Britain to seek peace terms
- But Falkenhayn's plan for an attack that would economise on German resources failed to work out as he expected, and he used many more divisions than planned
- Germany, like France, accumulated huge losses and gained little territory, leading it to throw more and more men into the conflict, and Verdun soon became a battle of prestige for the Germans, as well as the French