What makes a castle different from a fortress

Bodiam Castle opens a discussion of why historians disagree over whether some sites qualify as castles. A castle is a medieval fortified structure associated chiefly with nobility, royalty, or military orders, but the category overlaps with palaces and fortresses. Windsor Castle and the Tower of London show how a castle can also be a residence, while a fortress need not have that residential function. Some castles served towns as defensive strongpoints and protected their armouries. The Ring of Iron sites contained residences, but those rooms supported military operations rather than serving primarily as personal homes. The conventional castle label still fits them.