<human>:  When did the Battle of the Somme start?
<bot>: The Battle of the Somme began on July 1st, 1916. It was the largest battle of World War I, and it took place on the Western Front. The battle was fought between the British and German armies. It lasted for 10 days, and it was the deadliest battle of the war. The battle resulted in more than a million casualties, including 600,000 British soldiers. The Battle of the Somme was so costly that it was dubbed "the black day of the British army."