In fortification, a bacule is a kind of portcullis or gate, made like a pit-fall, with a counterpoise, and supported by two great stakes. It is usually made before the corps de garde advancing near the gates.
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This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed (1728). "article name needed". Cyclopædia, or an Universal Dictionary of Arts and Sciences (first ed.). James and John Knapton, et al.
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The original article can be found at Bacule and the edit history here.