National histories are framed by collective memories and political identities. They are transformed as much by changing events as by fresh historical investigation and revision.
Ireland's recent and not so recent past has provided graphic instances of this general phenomenon. They are exemplified in our recollections of, and attitudes towards, this country's participation in the first World War, out of which this State was born.
The Battle of the Somme, commemorated in a special supplement with this newspaper today, symbolises a side of that involvement which became excluded from the new State's collective memory, just as much as it was inscribed in that of Northern Ireland.
The recent transformation of relations between them and Britain through the Belfast Agreement allows this common history to be examined anew and to be publicly acknowledged in a completely different way. This weekend a State ceremony at the War Memorial Gardens in Islandbridge, Dublin will express "the shared history and shared experiences of the people of this island, from all traditions, in the year of 1916", as Taoiseach Bertie Ahern said at the launch of a commemorative stamp on the Somme last week.
In Ireland the Somme was closely interwoven, politically and historically, with the Easter Rising in April. By the time the battle started on July 1st 1916 attitudes towards the war had undergone a decisive change in the South, in response to the execution of the Rising's leaders. The British government's proposal to exclude six Ulster counties from the plan for Home Rule laid the groundwork for the later partition.
As a result the tens of thousands of Irish people who fought and died in the battle against the German army were fighting for very different - and rapidly changing - visions of Ireland's future. This supplement draws on recent historical research to explain this political context and how it was transformed in later years when the two new states emerged from the war.
It describes how a complex reality was simplified, distorted, its memory forgotten, suppressed and denigrated so that historical amnesia rather than recollection prevailed. It has taken courageous work by dedicated individuals and political leaders to remember it afresh in the Republic and to refocus collective memory in Northern Ireland away from a parallel political mythology there.
Ninety years on, the Somme's horrors and poignancy have not lost their evocative power. Its million casualties were victims of industrialised warfare on a scale never seen before.
The story of military attrition through mass slaughter presaged many of the 20th century's later barbarities. It was woven from a mixture of individual heroism, intimidation and suffering that is difficult for later generations to understand. This supplement is a contribution to Ireland's re-imagination of the Somme.