On the 90th anniversary of the epic first world war battle, this website examines what happened and why and remembers the irish who fought and died on that grim battlefield

Why we remember

How could well over a million men be killed or wounded for the taking of a few kilometers of ground? Fintan O'Toole on why it is essential that we remember the Battle of the Somme and the Irish who fought in it and first World War generally

You can still see the crater, 40 feet deep and 300 feet wide. And you can see what caused it in the film that is used in almost every documentary about the first World War.

The camera was set up to record the moment when the glorious victory was to begin, the explosion of one of a series of huge mines that signalled the start of the joint British and French offensive against the Germans. This one went off ten minutes early, at twenty past seven on the morning of July 1st, 1916, making it the inadvertent herald of the apocalypse that was to come: the Battle of the Somme.

The film captures the pure, primal energy of destruction. The terrible rumble of the earth and the rising pall of atomised earth have the same awful resonance as the images of the first nuclear explosion in the New Mexico desert. The famous words uttered by Robert Oppenheimer on that latter occasion would, in retrospect, have been even more apt on July 1st, 1916. The verse from the Bhagavad-Gita from which Oppenheimer quoted reads: "I am become death, the destroyer of the worlds, who has come to annihilate everyone. all those arrayed in the two opposing ranks will be slain!"

The Somme, along with the wider world war of which it is the epitome, was more than an episode of extreme violence. It changed the way the human species thinks about itself. The optimism of the 19th century, the belief that progress was inevitable and that humanity was on a straight road to civilisation, was blown apart in those explosions, sunk in the blood-soaked mud of the Somme, caught on the barbed wire of massive, pitiless and futile slaughter. Before the war, Sigmund Freud suggested that the basic human instinct was the sexual impulse, Eros. After it, he felt compelled to revise his theories and include a second, equally potent instinct, Thanatos - the death-wish.

How, other than through some quirk of human nature that made us desire our own destruction, could the Somme be explained? How was it possible that, after the carnage of the first day, when rank after rank of men walked towards the German machine guns and were mown down like grass, other men would repeat that walk of death day after day, week after week, until the middle of November, when the battle was stopped, not by the dawning of reason and humanity, but by the weather. How could well over a million men be killed or wounded for the taking of a few kilometres of ground? The nihilistic answers that proposed themselves - that violence and obedience were essential human traits - in turn went on to shape much of the 20th century, with its industrial murder, its cults of dictatorship, its life-and-death struggles, its gulags and its concentration camps. By discrediting the claims of enlightenment, democracy and civilisation, the Somme and its counterparts left an open space for barbarism to occupy.

Because it had such a huge impact on human self-understanding, the Somme ought to have been a part of Irish official memory, even if not a single Irish soldier had taken part. That in fact Irish involvement in the Somme was at least as prominent in proportional terms as that of any of the other combatant nations ought to have assured it a prominent place in our sense of our collective past. Yet, for at least 70 years, the memory of the Somme gave way to other battles of remembrance, as competing versions of Irish history dug their own trenches.

As so often, those apparently opposed versions in fact offered mutual reinforcement. The Somme, and especially that first day when the 36th (Ulster) Division took 5,000 casualties, did of course become a central part of the Ulster Protestant self-image. But it was absorbed into a partial and sectarian exercise in selective memory that was itself a kind of forgetfulness. How many of those who made their stand at Drumcree church in Portadown in the sectarian cold war of the 1990s remembered that the parade was supposed to be a commemoration of the Somme?

IN SOME WAYS, THE Somme posed as many challenges to Unionist as it did to nationalist orthodoxy. In order to remember the battle as a glorious sacrifice (contrasted to the stab-in-the-back of treacherous Catholics in the Easter Rising), it was necessary to forget its essential obscenity. In order to use the memory of the Somme to bolster obedience to authority, it was necessary to forget that the courage and self-sacrifice of the troops was betrayed by the folly of their leaders. In order to use the Somme as a marker of Protestant character, it was necessary to forget, not merely the presence of Catholic nationalist divisions, but also the fact that the Ulster Division had fought in what was seen as a typically "Irish" way. It lost so many men because those men ran with reckless zeal into the German lines, and were then forced to beat a bloody retreat. As Fran Brearton has pointed out, "The stereotype of the martial Irishman - valiant, aggressive, heroic, with a daredevil spirit - is seemingly remote from the stereotype of the Ulster Unionist - entrenched, defensive, immovable. The first of July points up the inadequacies of those stereotypes."

But nationalist orthodoxy was happy to leave the Somme to the Unionists, and to define it as an essentially British concern. This was not just amnesia, it was deliberate oblivion. When Ireland's most popular dramatist, Sean O'Casey wrote a play about the first World War, The Silver Tassie, in 1928, it was rejected by the Abbey. When the descendants of Thomas Kettle, a prominent nationalist intellectual and MP killed on the Somme, proposed the erection of a small monument to his memory in St Stephen's Green in Dublin, the project was delayed for 20 years because the Commissioners for Public Works would not countenance three simple words: "Killed in France".

Yet those words are written on the hearts of hundreds of millions of Europeans and hundreds of thousands of Irish people whose ancestors slaughtered each other on the Somme. We, who remember so much that is trivial and useless, cannot afford to forget them, for they give us a vital warning of the consequences of big-power games, fanatical nationalisms, and the abuse of human courage.

If we can forge a common clear-eyed memory of the Somme, we make it, not just an exemplar of those poisonous forces, but an antidote to them.