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 primary invention that rendered traditional stone castles obsolete was gunpowder, specifically when utilized in the form of powerful siege cannons. While stone fortifications had successfully withstood trebuchets and battering rams for centuries, the 15th-century advancement in artillery meant that heavy iron or stone balls could be fired with enough velocity to shatter even the thickest vertical masonry. As cannons became more mobile and accurate, the "high, thin" curtain walls of medieval castles became liabilities rather than assets. This technological shift forced a total redesign of defensive structures, leading to the rise of "star forts" (trace italienne), which featured low, thick, angled walls of earth and brick designed to deflect cannon fire rather than absorb it. By the 16th century, the castle had largely transitioned from a military fortress into a grand residence or "château," signaling the end of the castle as the dominant center of defensive warfare.