Various ceremonies were held across Europe to commemorate the 100th anniversary of the outbreak of World War I (WWI).
The lights across Britain were dimmed to pay tribute to about 17 million soldiers and civilians who perished in the brutality of the Great War that happened between 1914 and 1918.
Wartime Foreign Secretary Sir Edward Grey had made a remark on the eve of the outbreak of the WWI, on 4 August 1914, "The lamps are going out all over Europe. We shall not see them lit again in our lifetime," according to Reuters.
The headquarters of the Football Association, the Imperial War Museums in London, Greater Manchester, the Houses of Parliament and the Tower Bridge were among the buildings that participated in the lights out ceremony, according to the BBC.
The Duke and Duchess of Cambridge, Prince of Wales and Prime Minister of the United Kingdom David Cameron attended the twilight ceremony that was held at the St Symphorien Military Cemetery near Mons, Belgium. Prince Harry unveiled a memorial arch in Folkestone, England.
Personalities from 83 countries were also part of the ceremony in Belgium, including Francois Hollande of France and Joachim Gauck of Germany.
The Duchess of Cornwall, Deputy Prime Minister Nick Clegg and Labour leader Ed Miliband attended the service of solemn commemoration at Westminster Abbey.
Scroll down to check out the photos of the ceremony:
People enjoy an artwork entitled "Spectra" by Japanese visual artist Ryoji Ikeda during "Lights Out", as part of commemorations to mark the 100th anniversary of the outbreak of World War One (WWI), in London August 4, 2014. Lights across Britain were being switched off for an hour on Monday night in a tribute to the dead of World War One, inspired by the prophetic observation of Britain's foreign minister on the eve of war 100 years ago. Spectra's illuminations will light up the London skyline for seven nights.Reuters
(2nd L-R) Britain's Prince Harry, Mons city mayor Nicolas Martin, Britain's Prince William (2nd R) and his wife Catherine, Duchess of Cambridge appear on a balcony at the Mons town hall with Belgium's outgoing Prime Minister Elio Di Rupo.Reuters
Queen Elizabeth attends a commemoration service at Crathie Kirk Church in Crathie, Aberdeenshire.Reuters
French President Francois Hollande (R), Belgium's Queen Mathilde (L) and Belgium's Prime Minister Elio Di Rupo (C) wave on a balcony at the city hall of Liege.Reuters
Belgium's King Philippe (back L) attends a ceremony at the Cointe Inter-allied Memorial.Reuters
Military personnel hold candles during a service for the Commonwealth to commemorate the 100th anniversary of the outbreak of World War One, in Glasgow Cathedral, in Glasgow, Scotland.Reuters
Veterans and soldiers march in the "Short Step" parade, during the ceremony.Reuters
French President Francois Hollande and German President Joachim Gauck (L) attend a ceremony to commemorate the centenary of the start of World War One at the Vieil Armand "Hartmannswillerkopf" battlefield in the Alsace region, 3 August 2014.Reuters
From Left to Right: Belgium's outgoing Prime Minister Elio Di Rupo, Britain's Prime Minister David Cameron, Belgium's Queen Mathilde and King Philippe, Britain's Prince William and his wife Catherine, Duchess of Cambridge and Britain's Prince Harry attend a ceremony at St. Symphorien Military Cemetery in Mons.Reuters
Belgium's King Philippe kisses a girl during a ceremony at the Cointe Inter-allied Memorial, commemorating the 100th anniversary of the outbreak of World War One.Reuters
Light is beamed into the sky from Trafalgar Square to mark the100th anniversary of the outbreak of World War One.Reuters
A message on a wreath laid by Britain's Prime Minister David Cameron is seen at the Cenotaph.Reuters
Some 600 balloons emblazoned with a poppy and the name of a fallen soldier flutter in the sky during the "Short Step" ceremony, to mark the 100th anniversary of the outbreak of World War One, in Folkestone, southern England.Reuters