Somme: Flower of a generation lost on these killing fields, says William at sombre vigil for fallen
The Duke of Cambridge has paid tribute to the soldiers killed 100 years ago in the Battle of the Somme, saying "we lost the flower of a generation".
William spoke of European governments "including our own" who failed to "prevent the catastrophe of world war", in a speech during a military vigil at the gigantic Thiepval Memorial to the Missing in northern France.
He was joined by the Duchess of Cambridge and Prince Harry for the event ahead of today's 100th anniversary of the start of the battle, which lasted 141 days and claimed hundreds of thousands of British, French and German lives.
In an address written by Birdsong novelist Sebastian Faulks, William highlighted the almost 60,000 British and Commonwealth casualties of July 1 1916, the bloodiest day in the history of the British Army.
William told the assembled guests: "We lost the flower of a generation; and in the years to come it sometimes seemed that with them a sense of vital optimism had disappeared for ever from British life.
"It was in many ways the saddest day in the long story of our nation.
"Tonight we think of them as they nerved themselves for what lay ahead. We acknowledge the failures of European governments, including our own, to prevent the catastrophe of world war."
William said that the event honoured the more than 72,000 men whose names adorn the Thiepval monument, whose bodies have never been found, and those laying in Commonwealth cemeteries that litter the fields of the former Somme battlefield.
He added: "Tonight, we stand here with a promise to those men: We will remember you. The gift you have given your country is treasured by every one of us this day.
"The sacrifice you made will never, ever be forgotten."
Before the vigil's start William, Harry and Kate had climbed to the top of Sir Edwin Lutyens' 45m (148ft) monument to view the battlefield.
They were told of the carnage of 100 years ago which claimed the lives of more than a million men on all sides.
Historian Dr Glyn Prysor, from memorial maintainer the Commonwealth War Graves Commission (CWGC), welcomed the royal trio to the site and showed them around, saying they had been "moved".
Dr Prysor said: "There are more than 72,000 names on this memorial, those who have no graves, and it's very hard not to be moved.
"Prince Harry said it was his first visit - I think it was a first visit for all of them.
"They remarked on how impressive the memorial was when they arrived.
"It's the largest Commonwealth War Graves Commission site in the world and I think every visitor is struck by the enormity of it.
"We were talking of the inscriptions and how it wasn't just for the missing but honoured the alliance between the French and British armies.
"We then walked up to the top of the monument and spoke about the challenge British soldiers faced on that morning and the experience of the German soldiers. This was a battle where French, English and Germans all fought fiercely and all suffered terrible losses.
"The battlefield was all around us and we talked about how remarkable it is to see this landscape restored after the devastation of the war.
"Prince Harry asked about the trees and whether they came later - which many of them did when this memorial was built.
"All the CWGC sites tell the story of the battle and incredibly poignant resting of all those who fell.
"I think it's great them coming here to this event and if this visit encourages people to come and reflect on those who lost their lives here it will be a very powerful legacy of the commemoration event."
Harry also spoke at the event, reading the poem Before Action, written by Lieutenant WN Hodgson of the 9th Battalion the Devonshire Regiment, who wrote it days before he was killed in action on July 1, 1916.
A benediction was also given by the Most Reverend Justin Welby, the Archbishop of Canterbury.