Our line of defense was strongly fortified.

我们的防线壁垒森严.

The city is strongly fortified by soldiers.

这座城池被卫兵把守得固若金汤.

Ours is a strongly fortified position and the enemy will never be able to penetrate even if they have wings.

我们的阵地是金城汤池，敌人插上翅膀也过不来。