Britain's most famous landmarks including the London Eye, Houses of Parliament, Downing Street and Gateshead's Millennium Bridge were plunged into darkness for an hour last night to mark the moment Britain first declared war on Germany in 1914.
The Prime Minister has visited a memorial to his great, great uncle Captain Francis Mount, who died on the last day of the Battle of Loos in 1915.
Almost 60,000 British servicemen are thought to have lost their lives during the two-and-a-half week battle.
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.