Natural indigo, derived from the plant genus <i>Indigofera</i>, was cultivated commercially in the tropics. With the discovery of synthetic indigo in 1890, the industry was doomed. Adolf Bäyer contributed to the discovery by determining the structure of indigo in 1883. He showed that indole was the building block of indigo. Karl Heumann, at Zurich Polytechnic, first synthesized indigo. The first commercial process used naphthalene as the raw material. The process was refined and by 1914 synthetic indigo had almost completely replaced natural indigo.