The Duke and Duchess of Cambridge and Prince Harry have paid an emotional tribute to the thousands of fallen soldiers who lost their lives in the Battle of the Somme 100 years ago. The royals attended a poignant vigil at the Thiepval Memorial in Picardy, France, commemorating the eve of the centenary of the start of the Somme offensive on July 1, 1916.

The 'memorial to the missing' honours the 72,000 British and Commonwealth soldiers, who were killed in a seven-day British bombardment, in which some 120,000 soldiers scrambled out of the trenches and went 'over the top' to be gunned down by their German counterparts. The memorial bears the names of the soldiers who lost their lives and have no grave.

Over a million soldiers were killed and wounded on both sides after the four-month battle, the bloodiest day in the history of the British Army.

Reflecting on the tragic loss of life on July 1 1916, in an emotive address penned by Birdsong novelist Sebastian Faulks, Prince 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 forever from British life.

Somme centenary commemorations
Soldiers take part in a vigil at the Stone of Remembrance on June 30, 2016 in Thiepval, FranceAFP/Getty

"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."

Somme centenary commemorations
Reflecting on the tragic loss of life on July 1 1916, Prince William said it was 'the saddest day in the long story of our nation'AFP/Getty

William, 34, read a passage by author Sebastian Faulks, while Harry, 31, recited Before action, a poem written by Lieutenant WN Hodgson of the Devonshire Regiment.

In a poignant moment in the proceedings, military personnel read extracts from letters during part of a military-led vigil as hundreds of gravestones were illuminated.

Earlier in the day, the royals climbed to the top of Sir Edwin Lutyens' 45m (148ft) monument to view the battlefield. It was the first time they had visited the site and the young royals were said to be 'moved' by the experience.

Somme centenary commemorations
Harry, 31, recited Before action, a poem written by Lieutenant WN Hodgson of the Devonshire RegimentAFP/Getty

Joined by the Prime Minister and 10,000 members of the public, including hundreds of schoolchildren, the royals dressed demurely for the sombre occasion, with Kate wearing a monochrome coat dress from Missoni, and a black pencil-skirt, reported the Mail Online.

The royal family have been leading the tributes with The Queen and the Duke of Edinburgh attending a service at Westminster Abbey. The Queen symbolically touched a wreath that was placed at the Grave of the Unknown Warrior where an overnight vigil will be held.

Somme centenary commemorations
Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge and Prince Harry attend the Somme Centenary commemorations at the Thiepval Memorial on June 30, 2016 in Albert, France.AFP/Getty

The Dean of Westminster, the Very Reverend Dr John Hall, said: "The Battle of the Somme is remembered as one of the most devastating of the First World War. The sacrifice of many thousands of lives in a battle which ultimately failed to achieve any serious breakthrough stands as a reminder of the suffering and loss involved in the First World War.

Somme centenary commemorations
Military Personnel read extracts from letters during part of a military-led vigil as the tombstones of fallen soliders are illuminatedAFP/Getty

'As we imagine the feelings of those preparing for battle, the vigil will allow us to reflect on the cruel effects of warfare and to pray for lasting peace and justice in the world. All will be welcome.'

Services will also be held north of the border to remember the 51 Scottish battalions that took part in the campaign, with Edinburgh Castle set to be lit up in red. The Duke and Duchess of Cambridge and Prince Harry will be joined by Prince Charles, the Duchess of Cornwall, and the Duke and Duchess of Gloucester for commemorations on Friday (1 July).

Somme centenary commemorations
The Duke and Duchess of Cambridge and Prince Harry attend part of a military-led vigil to commemorate the 100th anniversary of the beginning of the Battle of the Somme at the Thiepval memorial to the Missing in June 30, 2016 in Thiepval, France.AFP/Getty