In military fortification, a boyau is a trench or ditch covered with a parapet that provided communication between two trenches, particularly the rear and front lines. Boyaus were typically constructed in a zigzag pattern to prevent exposure to direct enemy fire from the front."http://www.cr.nps.gov/hps/hli/currents/earthworks/glossaryA_C.htm Military Earthworks Terms". Historic Landscape Initiative, National Park Service.