Alexander Anton Bertholdt Merensky, missionary and author, grew up in an orphanage in Berlin. He was trained at the institute of the Berliner evangelischen Missiongesellschaft (Berlin Missionary Society) for three years, but also studied surgery and nursing at a hospital. In December 1858 he left Amsterdam for South Africa and, after getting acquainted with existing missions and the nature of the work, he and Reverend C.H.T. Grutzner established a mission station among the Pedi at Gerlachshoop, near present Groblersdal, in August 1860. Three years later Merensky married Marie Liers, with whom he had seven children. One of their sons, Hans Merensky*, became a well-known geologist.
After the Gerlachshoop mission was destroyed during a Swazi raid in 1864 Merensky bought a farm near Middelburg and in February 1865 he and Grutzner established the Botshabelo mission station there. It became a model settlement and the centre of the Berlin Mission in the Transvaal. Early in 1877 Merensky acted as mediator in the peace negotiations between President Burgers's forces and the Pedi Chief Sekhukhune. After some further medical studies in Pretoria he was admitted to practice medicine in the Transvaal and during the First Anglo-Boer War (1880-1881) served as a doctor to the Boer forces on the Natal border. At the end of 1882 he retired and returned to Germany.
Rumours of extensive prehistoric ruins north of the Limpopo inspired Merensky to study native folklore and historical manuscripts in an effort to establish their location. He gave his information to Karl Mauch*, who used it to locate the ruins of Great Zimbabwe in 1868. Merensky's main scientific interest was in geography and that same year Friedrich Jeppe* and he compiled the Original map of the Transvaal or South African Republic on a scale of 1:1 850 000. The scale has been described as unusual (Watson, 1968) but was no doubt intended to represent one arc-minute per millimeter (or 2.5 German geographical miles per centimeter). This topographical map was the first of its kind compiled locally from farm diagrams and other information, including a compilation started in 1866 by Mauch. There was as yet no triangulation on which it could be based, and it contained no contours or spot heights. None the less it was surprisingly accurate and by far the best map of the territory up to that time. It was published in Petermann's Geographische Mitteilungen (1868, Vol. 24). Petermann added some information to the map that was not locally available.
Seven years later Merensky published his improved Orininal map of the Transvaal or South African Republic, including the gold- and diamond-fields (Berlin, 1875). This was a more complete edition of the 1868 map, including information gathered by explorers such as Mauch, Eduard Mohr*, and J. Thomas Baines*. Upon his return to Germany he produced an Original map of South Africa containing all South African colonies and native territories (Berlin 1884), scale 1:2 500 000, on four sheets, covering the sub-continent up to 15o S.
Merensky was appointed to administrative posts until he was sent to Nyasaland (now Malawi) in 1891 to establish the Berlin Mission's first stations there. He visited the Transvaal before returning to Germany at the end of 1892. Based on this second period in Africa he compiled some small maps of the Shire Highlands and of present Malawi as a whole. His final cartographic work was an atlas, Mission-Atlas ueber die Arbeitsgebiete der Berliner evangelischen Missiongesellschaft... (1900), containing ten main maps and many smaller ones covering all the society's mission areas in Africa and China.
Merensky wrote extensively on a variety of topics. In 1884 he became a member of the Gesellschaft fuer deutsche Kolonisation and started contributing articles to the Deutsche Kolonialzeitung. While most of these dealt with the relations between European settlers and the native inhabitants of Africa and other aspects of colonisation, some related to topics of scientific interest, for example, "Die klimatischen Verhaeltnisse Transvaals" (1886), "Die Goldfelder im noerdlichen Teil des Matebelenreiches" (1888), "Die Akklimatisation des Pferdes in Suedafrika" (1888), and "Der Kohlenfund in Deutsch-Ostafrika" (1896). Book-length publications by him included Beitraege zur Kenntniss Sued-Afrikas, geographischen, ethnographishen und historischen Inhalts (1875), and Erinnerungen aus dem Missionsleben in Suedost-Afrika (Transvaal), 1859-1882 (1888). He spoke at medical meetings on tropical diseases and, in addition to his religious articles, published "Bemerkungen ueber die Natur und Behandlung des afrikanischen Malariafiebers" in the Berichte der Berliner Missionsgesellschaft (1893). Two other papers on medical topics, "Beobachtungen ueber die Wirkungen des Eukalyptus globulus bei paralytischen Zustaenden" (1882) and "Lepra unter der Zulubevoelkerung der Natalkolonie" (1885) appeared in Acta Leopoldina.
Merensky was an outstanding pioneer missionary, at home in the veld, a good horseman and hunter, hardy and undaunted, yet eloquent and persuasive, and driven by unshakeable religious zeal. His work was highly regarded. Honorary doctoral degrees were conferred upon him by the Universities of Heidelberg (Dr Phil, 1882) and Berlin (Dr Theol, 1899), and he was elected an honorary member of various academies and societies.