The outer defensive wall or rampart of a castle or fortified medieval structure.
From Norman French 'bailey' (outer wall), derived from Old French 'baile' (enclosure). Related to 'bailey' in 'motte-and-bailey' castles.
A ballium was medieval architects' answer to the weak spot in castles—an outer wall you could lose in battle while keeping the main keep safe and holding your enemies back.
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