Most people think that gunpowder was the cause of castles extinction. That is not true. Gunpowder changed their shape and design from the XIVth to the XVIII century. First they became rounded, so cannonball would deflect more often. read more
There is a slight caveat to this though. Castles were only ever a delaying tactic against an army with siege equipment. Castles and Burghals were primarily to defend against light and quick moving raiding parties like the Vikings and also to trap an invading army until an opposing army could be gathered to fight them. read more
Castles had been shown to be unable to resist modern cannon. By the 1520s, the "Trace Italienne" or "Star Fort" had been developed as an effective defense against cannon. Over the next 100 years, these forts spread across Europe and around the world. read more
Castles were great defenses against the enemy. However, when gunpowder was invented the castles stopped being an effective form of defence. By the end of the 1300s gunpowder was widely in use. The medieval castle with its high vertical walls was no longer the invincible fortification it had been. read more