Alexander Mack, who had come to Schwarzenau from Schriesheim near Heidelberg, founded a new radical Pietist movement in 1708, which is now known as the Church of Brethren and is one of the oldest churches with a free church tradition. Mack baptized seven adults at this point on the Eder by immersing them three times.
A memorial plaque commemorates the tolerance shown to the religious refugees by the sovereign, which made the founding of this church possible.
Between 1719 and 1735, the "Schwarzenauer Tunker" emigrated to America and today have more than two million members worldwide.
Even today, descendants continue to come to Schwarzenau to be baptized in the Eder.