The Collaborative International Dictionary of English v.0.48:

Vallar \Val"lar\, a. [L. vallaris.]
   Of or pertaining to a rampart.
   [1913 Webster]

   Vallar crown (Rom. Antiq.), a circular gold crown with
      palisades, bestowed upon the soldier who first surmounted
      the rampart and broke into the enemy's camp.
      [1913 Webster]