Plural of bastion; projecting structures in fortifications, or figuratively, things that defend or protect something important.
From French bastion, derived from Italian bastione, from Old Italian bastir (to build). The word originally meant a fortified outpost and evolved from military architecture into figurative usage meaning 'a source of protection or strength.'
Universities are often called bastions of free thought, free press is called a bastion of democracy—the word moved from literal castle features to metaphorical strongholds of values we want to defend.
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