Battle of Somme: Overnight vigil marks centenary
An overnight vigil is taking place in County Down to mark the beginning of the Battle of the Somme 100 years ago.
The event, at the Somme Museum near Newtownards, is open to the public and began at 19:00 BST on Thursday.
Similar vigils will be taking place in Cardiff, Edinburgh and London.
The Queen and Duke of Edinburgh are to attend a service at the grave of the Unknown Warrior in Westminster Abbey. The vigil at the Somme Museum will be held outdoors.
A guard of honour is to be present throughout the night and will include serving soldiers.
It will end with a service on Friday morning which will include the blowing of whistles at 07:28 BST - the exact time when the advance was signalled to begin one of the bloodiest battles in human history.
Nearby, a lone piper played a lament on Helen's Tower on the Clandeboye estate near Bangor on Thursday night.
Soldiers from the 36th Ulster Division trained on land around the tower before heading to battlefields of France
BBC News NI's Ciaran McCauley in Thiepval
About 2,500 people will congregate on Friday at the Ulster Tower in Thiepval, a quiet corner of northern France.
With just hours left until the commemoration marking 100 years since the Battle of the Somme, final preparations are in full swing.
Scores of soldiers march to and from the tower and the Royal Irish Regiment band tunes up for a rehearsal.
The world's media ready themselves to capture the sights and sounds of the anniversary event.
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Thousands of soldiers from across Ireland were killed at the Somme, 2,000 of them from the 36th Ulster Division died on the first day of the battle.
The Ulstermen who gave their lives in the World War One will also be commemorated in France, at the Ulster Memorial Tower, close to the village of Thiepval, which is a copy of Helen's Tower.
The tower, which stands 70ft (21m) in height, was built in 1921.
It was the first official memorial to be erected on the Western Front, according to the Somme Association charity, which has responsibility for maintaining the monument.
Families of soldiers who were killed in the battle have also started arriving in France ahead of the Somme centenary commemoration in Thiepval on Friday.
Brian Hewitt from Banbridge , County Down, has made the journey to pay tribute to his great, great uncle William James Allen, who fought with the 9th Battalion, the Royal Irish Fusiliers.
Pte Allen was originally from Portadown, County Armagh, but was living in America when he enlisted in the British Army.
He was killed in action on the opening day of the Somme.
Mr Hewitt plans to place a cross on the Thiepval Memorial in his honour, during the centenary commemorations.
"My father was to do it five years ago but died beforehand, before he could get over, so I'm going to fulfil a family ambition," he said.
The Foys from County Cavan flew into Paris last night.
Lucas Foy said he wanted to see the graves of the men who farmed the land close to him in County Cavan, before they lost their lives on the front line.
He said: "They (the men) didn't know what they were going to. They thought they'd be home in no time."