The myopic and colour blind Schiaparelli (neither of which, in all seriousness, hampered his renown as a meticulously observant astronomer) included in his map -- which he continued to augment all through the 1880s, and which served as the cartographic authority on the Martian landscape in planetary astronomy for two decades -- linear features that he saw criss-crossing the surface of Mars, which he referred to as 'canali'. This Italian word translates to English as either 'channels' or 'canals', and although Schiaparelli was implying the more naturalistic descriptor, 'channels', somehow 'canals' became the accepted terminology.

Via Bibliodyssey