CONTRAVALLATION
n.[L., to fortify. ] In fortification, a trench guarded with a parapet, thrown round a place by the besiegers, to secure themselves, and check the sallies of the garrison.
Con `tra *val *la "tion, n. Etym: [Pref. contra- + vallation: cf. F.contrevallation. Cf. Countervallation. ] (Fort. )