

Last Monday morning in Ypres, or “Wipers” as it was known by the British and Commonwealth soldiers, the flow of traffic through the vast Menin Gate at the entrance of the old Belgian town was stopped to allow the Last Post ceremony to be performed.



It was the 90th anniversary of the inauguration of the great white gate, the first memorial to the missing, built on the route marched by the soldiers on the way to the frontlines of the first world war.



The Belgian defence minister, Steven Vandeput, warned of the need to remember the sacrifices, particularly in today’s turbulent times, and a small crowd braved the drizzle to stand in silence in front of the huge Portland stone arch bearing the names of 54,392 men who fell but who were never found.



Facebook Twitter Pinterest French troops wearing an early form of gas mask in the trenches during the 2nd Battle of Ypres. Photograph: Hulton Archive/Getty Images

Then they listened to the bugles and a piper sound their lament for those who died in Flanders Fields. It was a familiar routine to Ypres’s 35,000 residents. Since 1928, a similar daily ritual has been performed at the stroke of 8pm by volunteers, a tradition broken only by a period of occupation in the second world war. Moving, but low key. This Sunday evening, however, things are set to be very different.

After 18 months of planning, the Prince of Wales, accompanied by the Duke and Duchess of Cambridge, William and Kate, are to join many thousands more in Ypres, including Theresa May, dignitaries from all the combatant nations, and an array of household names from stage and screen, to pay what is most likely to be the final great act of remembrance, in the presence of the sons and daughters, nieces and nephews of the hundreds of thousands of allied soldiers who died in the blood and mud of the Ypres salient.



Three horrific battles were fought for little gain here, of which the third and final was launched 100 years ago on Monday. “I died in hell – they called it Passchendaele”, the soldier and poet Siegfried Sassoon wrote of the carnage that raged between 31 July and 10 November 1917.



There were more than 320,000 allied casualties. German losses are estimated to have been between 260,000 and 400,000. The allied victors had made just five miles (8km) of ground when all was said and done, and still today the remains of around 30 soldiers are found every year, to be identified initially by the boots they were wearing when they died, said Peter Francis of the Commonwealth War Graves Commission. “A more sacred place for the British does not exist in the world,” concluded Winston Churchill in 1919.

Five years ago, David Cameron announced that fines retrieved from the banking sector following the financial crisis would fund a wealth of first world war centenary commemorations, including large-scale events.



Gallipoli, Jutland and the Somme have been remembered so far. This Sunday evening, as the sun goes down, the duke and duchess, along with the king and queen of Belgium, will join 200 descendants whose ancestors’ names are engraved on the Menin Gate. Prince William will say a few words, alongside the king, and they will lay a wreath before the bugles sound. Later that evening the royal couple will join a crowd of 8,000, perhaps more, in Ypres’s rebuilt market square to watch the story of the four years of war on a huge stage that took 10 days to erect.



Facebook Twitter Pinterest Rehearsals for the production of War Horse at the National Theatre, London, based on the novel by Michael Morpurgo. Photograph: Graeme Robertson/The Guardian

Performances and music will be set to a backdrop of light projections on to the huge Cloth Hall. A new short tale from the creator of War Horse, the author Michael Morpurgo, will be acted out, accompanied by a live narration from the actress Helen Mirren. Extracts from The Wipers Times, the play by Ian Hislop and Nick Newman based on the satirical trench newspaper published by British soldiers, will be read to the crowds. The spectacle will be shown live on the BBC.

It was in the early hours that the British infantry launched their attack in 1917. At a rather more civilised hour on its anniversary on Monday morning, 4,000 direct descendants of the battle of Passchendaele will join Prince Charles to attend a ceremony at the Commonwealth War Graves Commission’s Tyne Cot cemetery, where almost 12,000 men are buried.



Facebook Twitter Pinterest Rows of headstones at Tyne Cot cemetery in Zonnebeke, Belgium, where almost 12,000 men are buried. Photograph: Jack Taylor/Getty Images

Serving military personnel and descendants will read out letters and diaries from their ancestors. The Royal British Legion has created memorial pins made from the mud of the battlefields for guests to wear.



Before meeting descendants of the soldiers and visiting the Welsh National Memorial Park and Artillery Wood cemetery, Charles will officially open both the nearby British memorial poppy garden and the Zonnebeke Church Dugout, a preserved first world war dugout that forms part of the Memorial Museum Passchendaele.



Facebook Twitter Pinterest Harry Patch, who fought at Passchendaele, at the Menin Gate in 2007 at the age of 109. Photograph: Rex

Peter Slosse, head of the tourist office in Ypres, said that while this might be the last great commemoration at Ypres, he felt the very name of the place would remain significant through the ages, and attract visitors. Numbers peaked in 2014 at around 800,000, dropping to 430,000 last year.



“This event is a great gift from the British,” he said. “The media attention will move on, of course. Visitor numbers will go down a bit, but I am sure people will still come here. They still go to Waterloo.”



Ypres’s notoriety was built not only on the ferocity of the fighting, and a victory won at such great loss, but by the conditions in which it was fought. Constant shelling churned the clay soil and smashed the drainage systems. Unprecedented levels of rain added to the chaos, with the mud eventually becoming so deep that men and horses drowned in it. The last surviving British combatant in the battle, Harry Patch, died in 2009 at the age of 111. Such was the trauma of his experiences, his family disclosed, that each year the old man had locked himself away in a private vigil for his fallen friends.