From BiblePortal Wikipedia

Trench [1]

( חֵיל , Cheyl,  2 Samuel 20:15, a wall, rampart, or bulwark, as elsewhere rendered; מִעגָּל , Magal,  1 Samuel 26:5;  1 Samuel 26:7; or מִעַגָּלָה , magaldh, 17:20, a wagon-rut, hence a defense formed by the vehicles of an army; Χάρξ ,  Luke 19:43, a Mound [Lat. Vallum ] for blockading a besieged city, formed of the earth thrown out of a moat and stuck with sharp sticks or palisades) is also a military term, and denotes one description of the approaches to a fortified town. They were anciently used to surround a town, to enclose the besieged, and to secure the besiegers against attacks from them. Trenches could not be cut in a rock; and it is probable that, when our Lord says of Jerusalem ( Luke 19:43), Thy enemies shall cast a trench about thee, meaning, "they shall raise a wall of enclosure," he foretold what the Jews would barely credit from the nature of the case; perhaps what they considered as impossible: yet the providence of God has so ordered it that we have evidence to this fact in Josephus, who says that Titus exhorting his soldiers, they surrounded Jerusalem with a wall in the space of three days, although the general opinion had pronounced it impossible. This circumvolution prevented any escape from the city, and deterred from all attempts at relief by succors going into it. (See Siege).