What are some of the greatest fortresses ever built (they have been successful in repelling invaders and/or are impressive in terms of their size and ingenuity)? - Quora

What are some of the best fortified historical fortresses in your opinion? - Quora

What are some fortresses that were built but never used in war? - Quora

What are some of the greatest fortresses ever built (they have been successful in repelling invaders and/or are impressive in terms of their size and ingenuity)? - Quora

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

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

What are some of the greatest fortresses ever built (they have been successful in repelling invaders and/or are impressive in terms of their size and ingenuity)? - Quora

What are some of the greatest fortresses ever built (they have been successful in repelling invaders and/or are impressive in terms of their size and ingenuity)? - Quora

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

What are some fortresses that were built but never used in war? - Quora