Something like that look good for a start, added contour lines.
Also entrenchments have always been used, even in the field of battle. During this age of revolution, they were really put into full potential. Waterloo, the different riots in Paris, Yorktown, Borodino. Most of the time, the two armies would entrench and fight over several days while marching troops across an open field littered with bodies of previous waves of men while being fired upon. Sometimes they would meet the enemy out in the open if both armies sent out men at the same time or sometimes as a quick counterattack if their line won the skirmish.