Where did the germans chose to build their trenches?

First trenches are dug on the Western Front

Explanation:

In the wake of the Battle of the Marne—during which Allied troops halted the steady German push through Belgium and France that had proceeded over the first month of World War I—a conflict both sides had expected to be short and decisive turns longer and bloodier, as Allied and German forces begin digging the first trenches on the Western Front on September 15, 1914.

the answer i chose to believe is 'harmony'