A shield wall (German schildmauer) refers to the highest and strongest curtain wall, or tower of a castle that defends the only practicable line of approach to a castle built on a mountain, hill or headland. German sources may refer to a shield wall that protects two or more sides as a Hoher Mantel or Mantelmauer, which is variously translated as "mantle-wall", "mantle wall" or "high screen-wall". There is often no clear, definitive distinction between a shield wall and a mantle wall.