French President Francois Hollande and British Prime Minister David Cameron have met at the site of one of the 20th century's bloodiest battles. More than 1 million were killed, maimed or missing at the Somme in 1916.
A lone bagpiper walked around the edge of a shell crater at Thiepval in northern France, which was followed by a main event attended by the British royal family, the French and British leaders as well as former German President Horst Köhler.
Earlier, Britain's Prince William, his wife Kate, and his brother Prince Harry also attended the start of an all-night vigil to mark the 100th year anniversary of the start of the Battle of the Somme.
Soldiers from the United Kingdom, France, Australia, Canada, Germany, India, Ireland, New Zealand and Pakistan took turns to stay awake until 7:30 a.m. (0530 UTC), the precise time that the battle began.
Beginning on July 1 and dragging on through November in 1916, the battle in rural northern France was one of the largest of World War I.
Little more than a week after Britain's vote to leave the European Union, Hollande highlighted the friendship that saw British and French soldiers fight side by side.
"I want to recall that it is the European idea which allowed us to overcome divisions and rivalries between states, and which has brought us peace for the past 70 years," Hollande said in a statement before the ceremony.
A generation lost to warfare
Virtually an entire generation was lost at the Battle of the Somme. Some 20,000 British soldiers were mowed down by automatic gunfire and artillery after a week of bombardment failed to destroy the German Reich's defenses. Another 30,000 were wounded and maimed in what remains the deadliest day in British military history.
The ensuing battles fought in trenches pitting men with bayonets against machine guns, came to symbolize the futility of the conflict.
"Imagine yourself, standing in a trench with water well over your knees... while thousands of unseen shells come shrieking and whining overhead," wrote Private Albert Atkins, who survived the war. "There is a very slight pause - then it bursts and a tearing, rumbling blinding crash... hurling thousands of red-hot splinters in all directions, killing or maiming all they happen to strike."
French President Francois Hollande, Prime Minister David Cameron, Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge and Prince Harry attend a service to mark the 100th anniversary of the beginning of the Battle of the Somme on July 1, 2016 in Thiepval, France
A solemn moment for European nations
The ceremony at Thiepval is one of six in France, while Britain observed two minutes of silence to recall the moment when British, Commonwealth and French forces went "over the top" a century ago.
Around 10,000 visitors are attending the commemoration ceremony under heavy security which has the rolling fields under lockdown, with only shuttles heading back and forth to the memorial.
In London, Queen Elizabeth II attended a service at Westminster Abbey Thursday evening, and laid a wreath of roses on the grave of the Unknown Warrior.
Last month, Hollande and German Chancellor Angela Merkel jointly commemorated the centenary of the Battle of Verdun, the longest of World War I. The leaders praised their countries' friendship, risen from the ashes of two world wars and strengthened through EU cooperation.
jar/mm/msh (AFP, dpa)