(n.) A bridge of which either the whole or a part is made to be raised up, let down, or drawn or turned aside, to admit or hinder communication at pleasure, as before the gate of a town or castle, or over a navigable river or canal.

Bifrost abatis advanced work balistraria bank banquette barbed-wire entanglement barbican barricade barrier bartizan bascule bridge bastion bateau bridge battlement breastwork bridge bulwark cantilever bridge casemate catwalk cheval-de-frise circumvallation contravallation counterscarp curtain demibastion dike earthwork enclosure entanglement escarp escarpment fence fieldwork floating bridge flyover footbridge fortalice fortification gangboard gangplank gangway glacis lift bridge loophole lunette machicolation mantelet merlon mound outwork overbridge overcrossing overpass palisade parados parapet pontoon bridge portcullis postern gate rampart ravelin redan redoubt rope bridge sally port scarp sconce span stepping-stone stepstone stockade suspension bridge swing bridge tenaille toll bridge vallation vallum viaduct work