The Collaborative International Dictionary of English v.0.48:

Bulwark \Bul"wark\, v. t. [imp. & p. p. Bulwarked; p. pr. &
   vb. n. Bulwarking.]
   To fortify with, or as with, a rampart or wall; to secure by
   fortification; to protect.
   [1913 Webster]

         Of some proud city, bulwarked round and armed
         With rising towers.                      --Glover.
   [1913 Webster]