Why is this city Köln called Cologne? like perfume, see Eau de Cologne.

Long ago.. The city was named Colonia Claudia Ara Agrippinensium in 50 AD.

Eau de Cologne (French: [o d(ə) kɔlɔɲ]; German: Kölnisch Wasser [ˈkœlnɪʃ ˈvasɐ]; meaning “Cologne Water”), or simply cologne, is a perfume originating from Cologne, Germany. Originally mixed by Johann Maria Farina in 1709, it has since come to be a generic term for scented formulations in typical concentration of 2%–5% and also more depending upon its type essential oils or a blend of extracts, alcohol, and water. In a base of dilute ethanol (70%–90%), eau de cologne contains a mixture of citrus oils including oils of lemon, orange, tangerine, clementine, bergamot, lime, grapefruit, blood orange, and bitter orange. It can also contain oils of neroli, lavender, rosemary, thyme, oregano, petitgrain (orange leaf), jasmine, olive, oleaster, and tobacco.

In contemporary American English usage, the term “cologne” has become a generic term for perfumes usually marketed towards men.