The summit of one of Europe's tallest mountains glows like the flame of a candle as the sun rises on a clear morning. The Matterhorn, famous for appearing on bars of Toblerone chocolate bars, reflects the vivid orange light at 5.37am. (Photo by Margarethe Jaeger/Solent News & Photo Agency)

A recruitment drive during the First World War at Trafalgar Square, London. (Photo by Central Press/Getty Images)

National Guardsmen are put through riot training in Boston's Commonwealth Armory on Friday, October 18, 1974. Massachusetts Gov. Francis W. Sargent called up the guard to quell school violence, but the city has been relatively calm and the guard has remained in the armories. (Photo by JWG/AP Photo)

People help a woman overwhelmed by emotion and the heat during the mass funeral, attended by tens of thousands of mourners, of 613 coffins of newly-identified victims of the 1995 Srebrenica massacre at the Potocari cemetery and memorial near Srebrenica on July 11, 2011 in Potocari, Bosnia and Herzegovina. (Photo by Sean Gallup/Getty Images)

The attendants of the Sumptha Raja, Agra Durbar. (Photo by Hulton Archive/Getty Images). 1873

(L-R) Zandea,18, and Jessica, 21, pose showing off their clothing backstage during a show featuring OPT jeans December 8, 2011 in Yangon, Myanmar. (Photo by Paula Bronstein /Getty Images)

A man takes a photograph of his friend as thick smoke rises from a fire, which broke out at oil wells set ablaze by Islamic State militants before they fled the oil-producing region of Qayyara, Iraq, January 28, 2017. (Photo by Muhammad Hamed/Reuters)