"The statute of limitations has been a huge impregnable wall," Professor Hamilton said.

It concluded that it was to be doubted whether "an impregnable wall can ever be created" except in "very special cases".

Above them, piled block upon gigantic block, rose the wall, towering and impregnable.

Only had they encountered the same impregnable wall of savagery.

Built in 1537 of brick, it has immense circular mural towers and massive, impregnable walls.

"She said she couldn't stand the pathetic spectacle of a man banging his head against an impregnable wall."

Perhaps it was their impregnable walls that lulled them into complacency.

They'd seemed impregnable, concrete walls packed with fill.

The thing was a wild gamble, but it was better to jar the building than to melt its almost impregnable walls.

They are a boundary, a dividing line, a wall impregnable and unscalable.