Eduard Heinrich Gustav Dannert, Sociale Verhältnisse d. Ovaherero, Dr., 1888; Heinrich Vedder, Maharero and his time in the light of the documents of his estate, Dr., 1929-1931; Missionary August Carl Heinrich Kuhlmann, Götter- u. Geistergfaube d. Herero, Dr., 1927; Report about the "Maharero-Dag" in Okahandja (hectograph.), 1966; 1 Otjiherero grammar, ms..;

Station see RMG 2.510 a-c; Documents on the Ownership, 1899-1909; Map of Okahandja and surroundings of E. Friedrichs, 1: 500000, 1904; Site plan d. Farm "Friedrichswald", 1: 100000, 1903; ground plan of the farmstead of farmer Ernst Friedrichs zu Katjapja, 1: 100, 1903;