Why did military engineers begin building lower fortifications in the 15th century?

In the 15th century, military engineers began building lower fortifications primarily as a defensive response to the development of effective, heavy siege cannon.1

During this period, the rapid advancement of gunpowder technology rendered traditional, high-walled medieval curtain walls highly vulnerable to battery. High, vertical stone walls were easily crumbled by cannon fire, as demonstrated by the rapid collapse of fortresses during the Hundred Years’ War and the French invasion of Italy in 1494.12

Engineers discovered that lower, thicker ramparts—often constructed of packed earth—were far more resistant to cannon shot than vertical masonry. These low-profile designs allowed the entire structure to be defended by artillery mounted on bastions, which could provide flanking fire to protect the fortress ditches. This shift marked the end of the medieval castle era and the beginning of modern military architecture, eventually leading to the development of sophisticated, star-shaped fortresses.123