After the 16th century, castles declined as a mode of defense, mostly because of the invention and improvement of heavy cannons and mortars. This artillery could throw heavy cannonballs with so much force that even strong curtain walls could not hold up.

The decline of the traditional medieval castle was primarily driven by the evolution of military technology, specifically the widespread introduction of heavy gunpowder artillery in the 15th and 16th centuries. Historically, castles relied on tall, vertical stone walls to prevent infantry from scaling them. However, high-velocity cannons and mortars could easily shatter these rigid structures from a distance. By the time of the Italian Wars (1494–1559), it was clear that medieval fortifications were obsolete. They were replaced by "Star Forts" (Trace Italienne), which featured low, thick, angled earthen walls designed to deflect cannonballs rather than resist them. Beyond military utility, the socio-economic shift from feudalism to centralized nation-states changed the needs of the elite. Building and maintaining a private fortress was prohibitively expensive, and as internal peace improved, the nobility preferred building grand, unfortified "Country Houses" with large windows and gardens that prioritized luxury and status over defense.