Burm

A berm is a level space, shelf, or raised barrier (usually made of compacted soil) separating two areas. It can serve as a fortification line, a border/separation barrier, in industrial settings, or in many other applications. The word berm originates in the Middle Dutch and German berme and came into usage in English via French.

In medieval military engineering, a berm (or berme) was a level space between a parapet or defensive wall and an adjacent steep-walled ditch or moat. It was intended to reduce soil pressure on the walls of the excavated part to prevent its collapse. It also meant that debris dislodged from fortifications would not fall into (and fill) a ditch or moat.

In the trench warfare of World War I, the name was applied to a similar feature at the lip of a trench, which served mainly as an elbow-rest for riflemen.

In modern military engineering, a berm is the earthen or sod wall or parapet itself, especially a low earthen wall adjacent to a ditch. The digging of the ditch (often by a bulldozer or military engineering vehicle) can provide the soil from which the berm is constructed. Walls constructed in this manner are an effective obstacle to vehicles, including most armoured fighting vehicles, but are easily crossed by infantry. Because of the ease of construction, such walls can be made hundreds or thousands of kilometres long.

...
Wikipedia