On 4 August next year, "senior British and German politicians" - almost certainly David Cameron and Angela Merkel - will meet at the end of a suburban cul-de-sac in Belgium.

They will gather on two large mounds of spoil, excavated from phosphate mines in the 19th century. Long ago, the mounds were planted with pine trees, cotoneasters, flowerbeds and lawns – and the bodies of 600 young men.

Near here, on the outskirts of Mons, German and British soldiers fought the opening battle of the First World War in August 1914. Nearby, they also fired their final shots of the war, several hours after the armistice had been signed, on 11 November 1918.

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The site of the "ceremony of British-German reconciliation", marking the centenary of Britain's entry into the first industrial war, will be the Saint-Symphorien military cemetery.

Saint-Symphorien is an excellent choice. First, it is the only First World War cemetery to contain roughly equal numbers of German and "British" graves: 334 "Britons" and 280 Germans. (The inverted commas are necessary as many of these bodies are Irish or Canadian.)

And second, Saint-Symphorien, though small, symbolises all four years of the war's mass slaughter. If you enter the main gate and turn right, you follow a lawn path through clumps of white British and grey German gravestones. You reach two rows of graves facing each other near the boundary fence. At the end of the right-hand row is Private John Parr, 16, from Finchley, a bicycle scout, who was killed on 21 August 1914, two days before the Battle of Mons proper. On the left, directly opposite, is Private George Ellison, 40, from Leeds, who was shot by a sniper 90 minutes before the war ended at 11am on the 11th day of the 11th month of 1918.

Privates Parr and Ellison were the first and last British soldiers to be killed in combat in the First World War. Between their graves there are seven paces and, metaphorically, 886,000 dead British servicemen.

That first and last should rest so close together is a macabre coincidence. Parr was buried by the Germans in 1915. Ellison's body was moved from a makeshift grave when the cemetery was taken over by the Imperial (now Commonwealth) War Graves Commission in the 1920s. It was many decades before the eerie juxtapositon of the graves was noticed.

Remarkable? Yes, but it is equally remarkable that the two graves, and the hundreds of thousands of other individual graves from the First World War, should exist at all.

Where, after all, are the soldiers who died at Waterloo? Or in the Crimean War? Or the American Civil War? Or the Boer war? The answer is that pre-1914, with scattered exceptions, dead "other ranks" were tipped into pits. The First World War was the first in history in which systematic efforts were made to give permanent, marked graves to dead soldiers – however lowly and whether or not they could be identified.

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The contrast between the blind slaughter which killed 10 million soldiers on all sides and the democratic respect for the humblest dead private is one of the great paradoxes of this most baffling of wars. Soldiers could be destroyed en masse, torn apart or liquidised by the new arsenal of high explosives, machine guns, poison gas, tanks, flame-throwers and war planes. But they were to be honoured individuals in death.

Almost all combatant countries established constellations of war cemeteries, but none did so as enthusiastically, and as painstakingly, as Britain and its Empire. The first impulse for permanent cemeteries came from the soldiers themselves, who created makeshift burial grounds with ragged crosses and inscriptions, sticks and tin helmets. It was a British civil servant, journalist and businessman-turned-wartime ambulance chief, Sir Fabian Ware, who pushed for these "soldiers' cemeteries" to be recorded and made permanent.

Ware founded the Imperial War Graves Commission in 1917. After the war, the writer (and war-bereaved father) Rudyard Kipling and the architect Edwin Lutyens were part of a study group which recommended that cemeteries in France, Belgium, Italy, Turkey and the Middle East should be preserved "in perpetuity" as the principal British Empire memorials of the war.

No bodies would be repatriated. All ranks would be treated equally. The grave-markers would be upright slabs, not crosses, to avoid giving the war a simplistic, posthumous sanctity. The cemeteries would have a standard design, with standard symbols and inscriptions, and would resemble English country gardens

Even unidentified soldiers were to be given individual graves. France invented the concept of the "Unknown Soldier". We have cemeteries full of unknown soldiers. In the biggest cemetery on the Somme battlefields (Serre Road No 2), 4,944 individual graves – almost 70 per cent – carry no name.

"It is easy to forget now how revolutionary the cemetery idea was," said Peter Francis, head of external communications at the Commonwealth War Graves Commission. "It came, I think, from a realisation that this war was different, in scale and character, to anything before. This was not a war fought by a largely unloved and little known professional army. It was fought, after its first year, mostly by volunteers – by fathers, sons and brothers."

Nonetheless, the commission's choices, endorsed by the imperial governments, angered many people. There were petitions and furious debates in parliament about the "no repatriation" rule and about the "unchristian" and un-triumphant cemetery design.

Others saw the rebuilt cemeteries and the large monuments listing the "missing" at Ypres and the Somme as an attempt to "prettify" or sweeten memories of an unforgiveable war. Siegfried Sassoon, in his poem "On Passing the New Menin Gate" complained about the "intolerably nameless names" on the Ypres monument: "Well might the Dead who struggled in the slime/ Rise and deride this sepulchre of crime."

Vera Brittain, in her classic civilian memoir Testament of Youth, describes her distress when she found that the original, chaotic "soldiers' cemeteries" had become neat rows of graves surrounded by flowerbeds.

In research on the cultural origins of the choices made by Ware, Kipling and the others, the US-based British academic Joanna Scutts found that the idea that permanent cemeteries abroad should be the principal British memorials of the war can be traced to the famous lines in Rupert Brooke's 1914 poem "The Soldier": "If I should die, think only this of me:/ That there's some corner of a foreign field/ That is for ever England."

By the end of the war, such a mawkish sentiment was felt to be inadequate but could not be rejected entirely. "The struggle was to find a form and language for remembrance that would comprehend the soldiers' disgust… but would avoid suggesting to the bereaved that their losses had been meaningless," reported Scutts.

In other words, the cemeteries should be ambivalent. They should "leave interpretation open". They should not glorify the war; nor should they imply that it had all been a pointless waste of young life.

The Cenotaph in Whitehall proclaims its dedication to the "Glorious Dead". No such words can be found in the Commonwealth cemeteries. "Glorious death" is too brittle a concept to survive exposure to rows of named graves – or thousands of graves with no names. The standard cemetery inscriptions are the more neutral "Lest we Forget" and "Their Name Liveth Forever More".

There are 940 Commonwealth First World War graveyards in France and Belgium, ranging from the 11,954 burials at Tyne Cot near Passchendaele to dozens of tiny battlefield cemeteries on the Somme. They are more visited today than ever before.

The beauty of the flower borders and the constant replacement of time-worn stones give them a poignant, unsettling freshness absent from the German and French cemeteries. Something about the cemetery design compels the visitor to think of the dead, not as Sassoon's "intolerably nameless names", but as husbands, friends, lovers, fathers, sons and brothers. Thus have the controversial choices made in 1919 been vindicated by time.

The First World War gnaws at our guts because it raises questions to which there are no easy answers. Why did an educated, enfranchised population tolerate mass slaughter for so long? Is it right to fight for what you believe in, even if you know that warfare leads to unimaginable indignity and suffering? At what point do you stand up to evil? How can you distinguish good and evil from nationalistic ranting and posturing? The young men in boaters and flat caps who volunteered in 1914 were driven by the conviction that Britain is always right as much as a belief in freedom and democracy.

And yet can we confidently state that they were not defending freedom? What would the world have looked like had German militarism triumphed over flawed democracy in 1914?

The First World War cemeteries compel the visitor to consider these questions and they defy glib replies – especially the Saint-Symphorien, with its half-British, half-German occupancy.

A tragic ambivalence was deliberately built – or "coded" in Joanna Scutts' word – into the "silent cities" of France and Belgium. It is a principle worth recalling before we plunge into orgies of either flag-waving or facile pacifism next year.

The soldiers' stories: The first and last British combatants

The first man: John Parr

John Parr never "fought" in the Great War. He never knew the world of trenches, barbed wire, mud, poison gas, aircraft or tanks. Parr, from Finchley in north London, was shot by advancing German troops as he scouted, on his bicycle, ahead of the deploying British Army on 21 August 1914, two days before the first British battle of the war near Mons.

Parr was 16. He had lied about his age when he gave up his job as a caddy at the North Middlesex Golf Course in Friern Barnet Lane and joined the Middlesex Regiment a year earlier.

For many months, the British Army failed to report that he was dead or even missing. His mother, Alice Parr, of 52 Lodge Lane, North Finchley, finally wrote a letter complaining that she had not heard from her son for months. The War Office replied gruffly that it could not help.

It was not until after the war that a soldier who had been on the same scouting mission confirmed the time of Parr's death. He was the first of the 564,715 British and Empire soldiers to die on the Western Front. No picture of him has ever been found.

The last man: George Ellison

A former miner, married with a small son, Ellison had been a regular soldier for more than a decade when he was posted to France in August 1914 with the British Expeditionary Force – what the Kaiser referred to as a "contemptible little army".

Ellison, then 36, was among the first British troops to fight in trenches, in late 1914. Very few of the original foot-soldiers of the expeditionary force were still alive and fit to fight by the time the armistice was signed at 5am on 11 November 1918. Private Ellison was one of them – and still a private, which may suggest something about his character or record.

For reasons that remain controversial to this day, the fighting continued for another six hours until the 11th hour of the 11th day of the 11th month. It is estimated that 11,000 soldiers were killed or wounded on that final morning.

Ellison, who had survived so much, was one of them. He was shot by a sniper while part of a patrol scouting on the edge of Mons – about two miles from where he is now buried – at about 9.30am on 11 November. He was the last British soldier to die in combat in the First World War.

There were, however, further casualties among the Canadians, who were fighting a little to the west.

Private George Lawrence Price, 25, of the 6th Canadian Infantry Brigade, was shot through the head at 10.57am, three minutes before the guns fell silent.

Price, the last British Empire soldier to die, is also buried at the Saint-Symphorien cemetery, 20 yards from the eerily adjacent graves of Privates Parr and Ellison.