Financed by the British, the industrial complexes were designed by German engineers and built by slaves from Chile, who also worked on the exploitation of the mineral used for the production of gunpowder and fertilizers. Between the end of the 19th century and the beginning of the 20th century, almost all of the world’s saltpeter came from the Atacama Desert. However, with the advent of synthetic ammonia, which made it possible to produce industrial fertilizers, saltpeter cities collapsed. The wealthy owners abandoned the mines, leaving Chilean slaves and the contaminated land behind. The saltpeter complexes of Humberstone and Santa Laura continued their exploration until the mid-1900s but were abandoned in 1960, becoming ghost towns that were later opened to tourism. During his dictatorship, Pinochet used the city of Chacabuco as a concentration camp which was surrounded by landmines that remain in place to this day. In 2005, Humberstone and Santa Laura were declared World Heritage Sites by UNESCO and in 2010, two strong earthquakes hit Chile, destroying some of the few remaining Salitrieras.