 However, the regional Board of Inland Revenue—the "Finanzamt Düsseldorf-Mettmann"—serves both the municipalities forming the district of Mettmann, as well as the city of Düsseldorf proper.In the nearby Neanderthal, in the summer of 1856, quarry workers discovered the fossilised remains of what became known as the Neanderthal man or "Homo neanderthalensis" in Feldhof cave.As of 1945, Mettmann's population rose as a result of the resettlement of people - most of whom considered themselves as having ethnic or cultural ties with Germany, and the arrival of migrant workers from the Mediterranean region .