During this destruction the villagers . . . relied on their ancient instinct for survival and retreated to the impregnable fortress of the mountain.
-- Suheil Bushrui and Joe Jenkins, Kahlil Gibran: Man and Poet
What Spinoza says of laws is equally true of party-platforms,--that those are strong which appeal to reason, but those are impregnable which compell the assent both of reason and the common affections of mankind.
-- James Russell Lowell, "The Election in November", The Atlantic, October 1860
