Optical illusions, produced by telescopic viewing of Mars with a resolution of poorer than about 100 km, first reported by Schiaparelli (‘canali’ is the Italian for ‘channels’) and especially championed by Percival Lowell (1855–1916). These observers produced maps of the martian surface showing interconnected networks of canals, implying the presence of intelligent life on Mars. The intelligence which devised the canals was, however, on the terrestrial side of the telescope.