Figure 2.
Trenches were dug in the fertile farmland along the length of the front, interrupted only by underground bunkers, called abri, or other fortifications. The injured were carried through, around, or across the trenches to clearing stations. Planks across the trenches were called duckboards. The goal was to deliver the afflicted to clearing stations, some 500 to 1000 yards behind the line of entrenchment.