This money was raised for the purpose of making Antwerp an impregnable fortress.

We could not do more within the granite walls of an impregnable fortress.

We pity the gringos if they should attempt to beleaguer this impregnable fortress.

I feel as though I am walking around an impregnable fortress.

Here the vital principle of his faithfulness was entrenched as in an impregnable fortress.

He added that Tibet must "form an impregnable fortress in maintaining stability".

The supposed impregnable fortress of Metz held out little longer.

He had seemed like an impregnable fortress, an ineradicable fact.

It was not "an impregnable fortress," as Micheli says it was considered.

I questioned Thuvia, asking her what enemies the therns could fear in their impregnable fortress.

He failed to capture the impregnable fortress of Dhuspas, in which Sharduris had taken refuge.

COMMENT From the outside, Kensington Palace looks sort of like a noble but impregnable fortress.

Ages ago, skepticism intrenched itself in an impregnable fortress: 'There is no criterion of truth.'

Had she built her fancied impregnable fortress upon sand?

Our footing was obtained in their impregnable fortress, and, exulting in our success, we dashed on.

His imagination, flowering at once into splendor, depicted it as some kind of an impregnable fortress.