The only words we can say to veterans are “thank you”, Theresa May has told a ceremony to mark the 75th anniversary of the Normandy invasion.
Her words were echoed by French President Emmanuel Macron, who told D-Day veterans gathered in northern France that we owe them “our freedom”.
The day of commemorative events began with a lone piper marking the moment the first UK soldiers went ashore.
Donald Trump later told US veterans they were “the pride of the nation”.
The US president was at a service at the US war cemetery at Omaha Beach.
Hundreds of veterans are gathered in Normandy for the anniversary of the largest combined land, air and naval operation in history.
The day’s commemorations mark key events in the operation, which was aimed at bringing an end to World War Two.
By night-time on 6 June 1944, about 156,000 Allied troops had landed on Normandy’s beaches, despite challenging weather and fierce German defences. Some had drowned when they were accidentally dropped off too soon in deep waters.
By the end of D-Day, the Allies had established a foothold in France and within 11 months Nazi Germany was defeated and the war was over.
At 06:26 BST – the exact minute the first British troops landed on the beaches in 1944 – a lone piper played on a section of the Mulberry Harbour in the town of Arromanches.
Mr Macron and Mrs May – in one of her final engagements as Conservative leader – were in Ver-sur-Mer to see the first stone laid for a memorial to commemorate the 22,442 British troops who died there in the summer of 1944.
The memorial, which overlooks Gold Beach, depicts three soldiers advancing across the beach.
Mrs May told the ceremony that she was humbled to be able to mark the moment with veterans, who belonged to a “very special generation”.
“A generation whose unconquerable spirit shaped the post-war world. They didn’t boast. They didn’t fuss. They served,” she said.
“And they laid down their lives so that we might have a better life and build a better world.
“If one day can be said to have determined the fate of generations to come in France, in Britain, in Europe and the world, that day was June 6, 1944,” she added.
Also paying tribute, Mr Macron said: “This is where young men, many of whom had never set foot on French soil, landed at dawn under German fire, risking their lives while fighting their way up the beach, which was littered with obstacles and mines.”
The French president went on to say he was proud to have worked with Mrs May.
“Leaders may come and go but their achievements remain. The force of our friendship will outlast current events,” he said.
Following the inauguration ceremony, Mrs May, the Prince of Wales, the Duchess of Cornwall, Labour leader Jeremy Corbyn and Scotland’s First Minister Nicola Sturgeon attended a service at the cathedral in Bayeux, the first city to be liberated by the invasion.
At the start of the service, a message was read out on behalf of Pope Francis, in which he said D-Day was “decisive in the fight against Nazi barbarism”. He also paid tribute to those who “joined the Army and gave their lives for freedom and peace”.
Labour leader Jeremy Corbyn said the service was “beautiful and inclusive”, in memory of those “who died in Normandy and ultimately helped to defeat the scourge of fascism”.
The service was followed by a ceremony at Bayeux War Cemetery, where many of the fallen are buried.
Meanwhile, US President Donald Trump accompanied Mr Macron at a ceremony at the US war cemetery at Omaha Beach, Colleville-sur-Mer.
He told veterans gathered there: “You are among the greatest Americans who will ever live. You are the pride of the nation. You are the glory of our republic and we thank you from the bottom of our hearts.”