What are/have been the most impregnable fortresses in history? - Quora

21 of the Great Fortresses Around the World

Could a modern military successfully invade and capture one of the castles or strongholds that were built during medieval times? - Quora

At what point in history were castles the best built and strongest? - Quora

What was the point of having fortified castles inside of fortified cities? - Quora

How common was it for the castle to be inhabited by no more than 4 people really? - Quora

What is/was the strongest fort/castle for defense from any era, preferably not English style? - Quora

Which castle has been the most successful throughout history at withstanding sieges? - Quora

Why did the middle ages castles have so many towers? - Quora

What are the most impressive castles and forts still standing? - Quora

What was the most defensible castle/fortress of pre-gunpowder Europe? - Quora

Why are most castles in Europe located on rocky hills? - Quora

What are the most impressive castles and forts still standing? - Quora

What are some of the most imposing castles around the world? - Quora