Refers to a terrain that is extremely strategic, rugged, and difficult to access or conquer, often implying an impregnable stronghold.
这座山城地处偏远，周围群山环绕，可谓是崤函之固，易守难攻。
This mountain city is remotely located, surrounded by mountains, making it an impregnable stronghold, easy to defend and difficult to attack.
Era:
Ancient
Frequency:
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