Messines was the first time the Irish and Ulster divisions fought together
Several hundred people have taken part in a remembrance service in the centre of Londonderry to commemorate the Battle of Messines in 1917.
Wreaths were laid at the cenotaph and there was a minute's silence.
Local students who were involved in a project on the battle also spoke of their experiences after a visit to the battlefield.
As part of the event the Union flag and Irish tricolour were given equal prominence throughout the proceedings.
Glen Barr, head of the International Peace Project in Messines, said that they had being parading in Belgium for the last ten years at it was time the service "came home".
"On a battlefield it didn't matter what religion you were it was about common humanity," he said.
On 7 June 1917, the British Second Army, under the command of General Herbert Plummer, launched the Battle of Messines, one of the bloodiest battles of the First World War.
The battle, months in the planning, centred around the strategically important Messines Ridge.
It was said that the sound of the mine explosions launched during the Battle of Messines could be heard as far away as Dublin.
More than 40,000 men lost their lives during the fighting.
The 16th Irish and 36th Ulster divisions fought side-by-side to capture the small town of Wystenchaete - the first time the two divisions had fought together.