The 50,000 Irishmen from north and south who died in the first World War will be commemorated this afternoon when the President, Mrs McAleese, and Queen Elizabeth take part in a historic ceremony in the Belgian village of Mesen (Messines).
The inauguration of a memorial peace park for the Irish dead will be "an important symbolic moment of reconciliation in our history", the Taoiseach said in a statement.
It was at Messines, near Ypres, that the 36th Ulster Division, drawn from the pre-war Ulster Volunteer Force, and the 16th Irish Division, largely drawn from the Irish National Volunteers, fought side by side in June 1917 and won a stunning victory.
Both divisions suffered heavy losses at several stages of the war. In the decades to come, the men of the Ulster Division were remembered as heroes within the unionist community in Northern Ireland; by contrast, the Irish Division, which suffered the heavier casualties, was barely granted a passing thought in the Republic until recent years, and survivors often suffered scorn and abuse.
Today's meeting between the President and Queen Elizabeth at a local airport before the ceremony will be the first official meeting between the two heads of state.
King Albert and Queen Paola of Belgium will also take part in the ceremonial opening of a peace tower - modelled on an Irish round tower - built by young work trainees from both sides of the Border.
The new Island of Ireland Peace Park is the brainchild of former Fine Gael TD for Donegal Mr Paddy Harte and the Derry community leader and former UDA political adviser Mr Glen Barr, together with the cross-Border Journey of Reconciliation Trust.
Also present at today's ceremony will be a group of 33 members of the Dublin Fusiliers Association, many of them relatives of men who died in the first World War. They are led by their chairman, Mr Tom Burke, whose researches into the Irish who fought have led to an exhibition currently on view at the Dublin Civic Museum.
His group will hold its own ceremony this morning, when it will lay wreaths at the Prowse Point military cemetery four miles from Messines and read out the names of some of the hundreds of Irishmen buried there.
"These are names which probably have not been mentioned for 80 years, names of young men from Drimnagh, Gloucester Street, Meath Street and Finglas, many of whom lied about their ages so they could go out and fight," said Mr Burke.
Meanwhile, the Department of Foreign Affairs has defended its decision to turn down an invitation for the Army band to play at a Last Post commemorative ceremony in Ypres last night. A spokesman for the Department said the band wanted to focus on the ceremony in Messines today and was busy yesterday practising with the British army band.
The spokesman said there was no political motivation behind its decision.