1.   An impregnable fortress that had foiled one invader after another over the centuries.

2.   As the dreamer bemoans his misfortune, an impregnable fortress is erected around the rosebush.

3.   It was as impregnable a fortress for the Israelis as it had once been to the knights of France.

4.   The lower figure indicates that Microsoft is not the impregnable fortress depicted at its trial, McKenzie writes in a paper.

5.   The lower figure indicates that Microsoft is not the impregnable fortress depicted in the antitrust trial, McKenzie writes in a paper that presents the results of his survey.

6.   Tora Bora seemed to be an impregnable fortress when Osama bin Laden controlled the high ground.

7.   Ali, who fought the Soviets from Tora Bora, described it as an impregnable fortress.

8.   Ali, who fought the Soviets from Tora Bora, has described it as an impregnable fortress.

9.   Former anti-Soviet fighters describe Tora Bora as an impregnable fortress that has never been taken by force.

10.   Local militia leaders in eastern Afghanistan suspect bin Laden may be holed up in a mountain base called Tora Bora that veteran Afghan guerrillas describe as an impregnable fortress.