The royal family has a personal connection to the brutal battle. Among those killed was Captain Henry Archibald Cubitt, a 24-year-old member of the Coldstream Guards and the great-uncle of Camilla, Duchess of Cornwall. He was the eldest of three brothers who died in area of the Somme – a battle that dragged on until November 18, 1916 – within 18 months of each other.
Speaking from the steps of the memorial, William offered his respects to the fallen.
"One hundred years ago tomorrow at 7:30 a.m. the British army attacked German lines across these fields. To the young men eager to fight it was known as the 'Big Push.' The joint British and French offensive intended to put unbearable pressure on the German army and hasten an end to the war.
"Most of those who went over the top that day were wartime volunteers. Some as young as 16. Some had already seen action. For others the Somme was their first experience of battle. By the end of the 1st of July the British Army had sustained almost 60,00 casualties, of whom nearly one third had died. 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. 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.
"We offer our humblest respects to each man who fought in the Battle of the Somme from every corner of the British Isles and from across the Commonwealth. We honor those whose names are recorded on this memorial. More than 72,000 who have no know grave. And to those who lie buried in Commonwealth war cemeteries.
"And tonight we stand here with a promise to those men. We will remember you. The gift you gave your country is treasured by every one of us this day. The sacrifice you made will never, ever, be forgotten."
William, Kate and Harry visited the top of the Thiepval Memorial to the Missing, a war memorial that honors the 72,195 missing British and South African servicemen who died in the Battle of the Somme.
Ceremonies today and tomorrow mark the 100th anniversary of the offensive and its deadly toll.