slighting

A slighting is the deliberate destruction of a fortification without opposition from its builders or last users.

Many European castles or forts were slighted in the Middle Ages by victorious besieging armies. Some were also destroyed by the owners themselves when they were abandoned to prevent potential enemies from possibly using the intact fortifications. The fortifications of many European cities were slighted in the 19th century because they no longer were effective defense structures and were obstacles to urban expansion.

Traditionally, a strategy of slighting fortifications was often adopted in warfare by the side which had the support of the ordinary population, against an opponent which may have been militarily strong but did not have popular support, often an alien invader. Examples of forces who adopted this strategy include the Bruce brothers in the Scottish Wars of Independence, the Mamelukes in their wars against the Crusaders, and the Parliamentary side in the English Civil War.

It has also been traditionally believed that a strategy of slighting was adopted by the Swiss in their rising against the Austrians (the rising associated with William Tell) but archaeological research suggests that many of these fortifications were destroyed before this rising.