Here are some of the key numbers from the battle of the Somme, which began 100 years ago on July 1:
7 - days of artillery bombardment of the German lines before the battle started, aiming to cut the barbed wire and destroy trench defences and artillery.
1,500,000 - artillery shells fired by the Allies in that week, to little overall effect.
57,470 - British casualties on the first day.
19,240 - British first-day casualties who died.
60 - percentage of British officers involved on the first day who were killed.
141 - days the battle lasted, from July 1 to November 18.
Somme selfies: long-lost photographs of British soldiers involved in the battle
419, 654 - official number of British dead, missing or wounded
1,300,000 - approximate number of casualties on both sides
6 - miles that British soldiers had advanced by the end of the battle.
49 - Victoria Crosses awarded for valour during the battle.
150,000 - graves in the area cared for in more than 250 military and 150 civilian cemeteries in the Somme area by the the Commonwealth War Graves Commission.
72,000 - number of British and Commonwealth soldiers who died at the Somme with no known graves and whose names are recorded on the British memorial at Thiepval.
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