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. Francois Hollande and Angela Merkel used Verdun as a symbol of both reconciliation between their nations and of EU integration. 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.