Ireland's Archbishop Eamon Martin has said prayers on the spot where Irish troops died at the Somme as he urged Catholics to remember the First World War.
The Irish primate commemorated the shared sacrifice with Protestants during a short memorial ceremony in the village of Guillemont at a stone Celtic cross commemorating the 16th Irish Division which fought a century ago.
Thousands of soldiers from across Ireland died or were wounded at the Somme as part of the British Army. The first day, July 1 1916, was the bloodiest in British military history.
Archbishop Martin said: "In remembering the horrors of the war a century ago it helps us to redouble our efforts towards building peace, healing and reconciliation.
"I know that we have gone our separate ways in many ways over the last decades in Ireland and the more recent conflicts have tended to divide us and we don't realise the shared narrative that there is in the sacrifice of those men in the First World War.
"So I am hoping that being here myself will give a signal to Catholics that it is okay for them to remember the First World War and I am hoping that it will also open up the Protestant community to realise that many Catholics died side by side with their ancestors here on these fields of France."
The 16th Irish Division went into battle on September 3 at Guillemont. The area was badly shelled throughout 1916 and was full of broken trenches and shell holes and very difficult to attack over, chairman of the Somme Association Alan McFarland said.
A total of 1,147 soldiers were lost out of the 2,400 who attacked.
Private Thomas Hughes of Castleblayney in Co Monaghan was awarded the Victoria Cross after he was wounded and went back into battle and single-handedly took out a German machine gun position and captured four German soldiers.
A few days later in a neighbouring village the Irish Division lost Professor Tom Kettle, an MP and noted poet who favoured Irish Home Rule.
Ulster Unionist leader Mike Nesbitt and council delegations from Lisburn and Portadown were among those who gathered for the service.
The Last Post and Reveille bugle calls were sounded and a piper played a lament before poppy wreaths were laid by the Somme Association, military figures and a series of local councils.
The Royal Irish Regiment (RIR) provided a ceremonial guard of honour.
Mr Nesbitt said the service commemorated men from Londonderry, the mainly Catholic Falls Road in Belfast and all over the island of Ireland.
"It reminds me as we struggle to create a shared future that we actually have the example of a shared past, of service and sacrifice.
"Of sacrifice in almost unimaginable numbers, not just the 36th Ulster Division, not just the Protestants and unionists from the north-east of Ireland but from all over the island who came here and fought and died together."