The Russian attack was spread over how long a line?

In order to relieve the German attack on Verdun, the Allies were to launch the Battle of the Somme in June 1916.  In an attempt to take German forces from the Western Front the Russians were also to launch an attack on the Eastern Front at the same time.  This was the Brusilov Offensive.  It was a victory for the Russians, though not as successful as hoped, and it ranks as one of the largest campaigns of the entire war.