The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "contravallation":
   abatis, advanced work, balistraria, bank, banquette,
   barbed-wire entanglement, barbican, barricade, barrier, bartizan,
   bastion, battlement, breastwork, bulwark, casemate,
   cheval-de-frise, circumvallation, counterscarp, curtain,
   demibastion, dike, drawbridge, earthwork, enclosure, entanglement,
   escarp, escarpment, fence, fieldwork, fortalice, fortification,
   glacis, loophole, lunette, machicolation, mantelet, merlon, mound,
   outwork, palisade, parados, parapet, portcullis, postern gate,
   rampart, ravelin, redan, redoubt, sally port, scarp, sconce,
   stockade, tenaille, vallation, vallum, work