Cascan

In fortification, cascans, or cascanes, are holes, or cavities in the form of wells, made in the terreplein, near a rampart; from which a gallery, dug in a similar manner underground, is conveyed, to give air to the enemy's mine.

 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.