要よう害がい堅けん固ご

noun, noun which may take the genitive case particle 'no'

impregnable; unassailable

Describes a fortress or defensive position that is naturally strong and difficult to attack. Often used in historical or military contexts.

• この城しろは要よう害がい堅けん固ごで、敵てきは容よう易いに攻せめられなかった。

  This castle was impregnable, and the enemy could not easily attack it.

• 要よう害がい堅けん固ごな地ち形けいを利り用ようして砦とりでを築きずいた。

  They built a fort taking advantage of the unassailable terrain.