The royals received a historical briefing on the battlefields of the Somme at Thiepval Memorial.
The trio looked across no mans land in Northern France.
The view from the top of the monument.
William, Kate and Harry viewed the battlefield site and heard a description of the events that took place there during the First World War.
Royal reporter Emily Andrews was on the ground with the royals and shared photos from the small town of Albert which had been gearing up for commemorative events throughout the day.
Rehearsals and preparations at Thipeval have been underway throughout recent days.
William, Kate and Harry attended a vigil at Thiepval Memorial. The Thiepval Memorial to the Missing of the Somme bears the names of more than 72,000 officers and men of the United Kingdom and South African forces who died in the Somme sector before 20 March 1918 and have no known grave. Over 90% of those commemorated died between July and November 1916.
The memorial also serves as an Anglo-French battle memorial in recognition of the joint nature of the 1916 offensive, and a small cemetery containing equal numbers of Commonwealth and French graves lies at its foot.
The memorial, designed by Sir Edwin Lutyens, was built between 1928 and 1932 and unveiled by the Prince of Wales, in the presence of the President of France, on 1 August 1932.
In the words of Sebastian Faulks, Prince William said:
'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.'
Prince Harry read W N Hodgson's Before Action, written just days before he died on 1 July 1916. "Tonight we think of them as they nerved themselves for what lay ahead."
James Grantham, of the King's Troop Royal Horse Artillery, is leading the all-night vigil at the Thiepval Memorial in France tonight, marking the centenary of the Battle of the Somme. According to the Minsitry of Defence: "He will be standing just feet away from the engraved name of his great uncle, Private George Henry Grantham, who died on the first day of the battle, 1 July 1916. RSM Grantham said the vigil will be an emotional opportunity for him to pay his respects to a relative who made the ultimate sacrifice."
The sun setting on Thiepval as British Armed Forces prepare to stand vigil overnight.
The Battle of the Somme was the bloodiest encounter in the history of the British Army. It took place between 1 July and 18 November 1916 on both sides of the upper reaches of the River Somme in France. It was the largest battle of the First World War on the Western Front; more than one million men were wounded or killed, making it one of the most brutal battles in human history. Shockingly, the infamous first day of the offensive saw British forces suffer 60,000 casualties of whom 20,000 died. It was the largest loss of life on a single day in British military history. Some 60 per cent of all British officers involved on the first day were killed, as Allied troops advanced slowly across no man's land through a hail of machine gun fire.
More from the Telegraph:
'The battle was planned to end months of deadlock on the Western Front, break through Germany lines and also relieve pressure on the French forces at Verdun - a nearby town that had been under siege.
Laden with heavy kit, the British infantry began their laborious advance at 7:30am on July 1 following a week of intense artillery bombardment of German positions from the village of Serre to Maricourt which had intended to annihilate enemy forces.There was a belief that following this bombardment, troops would take a safe stroll across no-man's land to trenches the Allies thought would be empty, but German defences were far better than they had anticipated.
German troops had hidden safely in deep dugouts during shelling the previous week and emerged quickly, catching the Allies by surprise and shooting them down in vast numbers. In the first 24 hours, there were 57,470 casualties (including 19,240 men killed) – just under half the total engaged. Most men were killed in the first few minutes.'
Commemorations were held far and wide to mark the anniversary. At Westminster Abbey Her Majesty and the Duke of Edinburgh led the nation's remembrance. The Queen laid a wreath on the grave of the Unknown Warrior. Her Majesty's grandfather King George V placed a wreath of roses and bay leaves on the coffin of the warrior 86 years ago. This evening, the wreath was also made of roses and bay leaves.
The Duchess wore the Missoni Long Snake Stitch Coat tonight (with thanks to Kate Middleton Style and Poppy G). Made in Italy, the coat features front button closure and patch pockets. It is described: "Silver metallic threads shimmer within the monochromatic hues defining a textured A-line coat that's visually shaped with an angled zigzag pattern." The £2,900 piece appears to be sold out for some time, but can be viewed at Nordstrom.
Kate wore a black dress underneath.
Readers will recognise Kate's large pearl earrings as the pair she wore for Trooping the Colour.
Kate wore a black pillbox hat - a style very reminiscent of Jackie O. and completed the look with her black Gianvito Rossi heels and black Mulberry clutch.
Tomorrow, William, Kate and Harry will open the new Thiepval Memorial to the Missing Visitors Centre. Afterwards, they will join other royals to attend the National Commemorative Event to mark the Centenary of the Battle of the Somme at the Commonwealth War Graves Commission Memorial.