Coupure

During a siege, a coupure is a ditch or an earthwork or wooden palisade built behind a breach made by the attacker's guns in the walls of a fortress or a city.

It can also be a passage through a glacis to create a sally port, so that the defenders can launch a sortie against the attackers.

More sophisticated means of closing a coupure consist of wooden or metal beams or doors.

Between the stacks of beams, which form two walls, horse manure or other animal faeces mixed with straw is dumped and compacted.

Stephen Francis Wyley A Dictionary of Military Architecture Fortification and Fieldworks from the Iron Age to the Eighteenth Century, Drawings by Steven Lowe