The ceremony was no doubt important for the Beefeaters, all of whom are veterans who served at least 22 years in the military.
Volunteers, many of whom had a family connection to the war, also helped the Beefeaters light the torches.
It took the group of Beefeaters and volunteers a little less than an hour to light the thousands of torches.
The torches burn for about four hours before running out fuel. They will be refilled ahead of each subsequent lighting.
World War I broke out in June 1914, when Serbian terrorists assassinated Archduke Franz Ferdinand, heir to the throne of Austria-Hungary.
Austria-Hungary declared war on Serbia, and allies of both countries entered the fray.
Britain joined the Serbian side that August, when Germany, an ally of Austria-Hungary, invaded Belgium, which the Brits had promised to defend under the 1839 Treaty of London.