antemural

from The Collaborative International Dictionary of English v.0.48

Antemural \An`te*mu"ral\, n. [L. antemurale: ante + murus wall.
   See {Mural}.]
   An outwork of a strong, high wall, with turrets, in front of
   the gateway (as of an old castle), for defending the
   entrance.
   [1913 Webster]