People should "never fail to cherish" peace, David Cameron said as he joined a twilight ceremony to mark 100 years since Britain joined the First World War.
Cameron told those assembled at St Symphorien military cemetery near Mons, Belgium: "This was a war with an immense human cost - and we must always, always remember that, no matter how busy things are.
"In shaping that future, it is vital that we look to the past. Here on the continent of Europe we saw not the war to end all wars, but the precursor to another desperate and violent conflict just two decades later.
"We should never fail to cherish the peace between these nations and never underestimate the patient work it has taken to build that peace."
As the Lights Out event to remember those who fought and died in WWI happened last night ITV asked our viewers what they did to take part.
Lights on some of Britain's most famous landmarks were extinguished between 10pm and 11pm to remember those who died in WWI.