From 《史记·天官书》: 海旁蜃气象楼台,广野气成宫阙 — ancient Chinese believed giant sea-clams (蜃) exhaled breath that condensed into phantom towers on the horizon; modern science identifies the phenomenon as atmospheric refraction.
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海 (sea) + 市 (market) + 蜃 (sea-clam) + 楼 (tower): 'a clam-breath city-tower over the sea.' Picture a shimmering phantom city that isn't really there.