Source : Webster's Revised Unabridged Dictionary (1913)

Contravallation \Con`tra*val*la"tion\, n. [Pref. contra- +
   vallation: cf. F. contrevallation. Cf. {Countervallation}.]
   (Fort.)
   A trench guarded with a parapet, constructed by besiegers, to
   secure themselves and check sallies of the besieged.