ISTANBUL—In this ancient city once ruled by sultans and emperors, the real king is the humble alley cat.

In historic neighborhoods along Istanbul’s Bosporus and Golden Horn waterways, an army of furry-tailed street cats are fed, sheltered and cooed at by an adoring public. Hundreds of fleece-lined houses have been erected at street corners by cat-mad residents. Most are flanked by makeshift feeding stations fashioned from yogurt pots or plastic bottles and overflowing with tasty scraps.

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