the germans began Process_start systematic fortification of the area , according to a directive from erich von falkenhayn the german army chief of staff , to fortify the western front so that a small number of infantry could defend Defending the front indefinitely and later in the year began Process_start work on second and third defensive positions but in the somme area , the defences north of the unk were improved Cause_to_make_progress first and by july 1916 the first position defences around mametz were extensive but the second position was a shallow trench and the third position had only been marked Recording out .