The reason why the texts on verso of the atlas maps written by one of the best studied cartographers, viz. Abraham Ortelius (1527-1598) of Antwerp in his Theatrum Orbis Terrarum of which the first edition appeared in 1570 have never been studied in the course of 450 years will probably remain an enigma. The research presented here tries to demonstrate that these texts contain many innovations in 16th century historical cartography. For this purpose, a sample of on verso texts as occurring on ten atlas maps from Ortelius’ Theatrum atlas has been examined and translated into modern English. In the course of making these translations, it became clear that these texts are a much more accurate method to date loose maps than by referring to the states of maps whose versos they adorn. It also became apparent that these texts belong to two types: scholarly texts which were written for the Latin atlas editions and for the Spanish, post-1573 German, Italian and English editions translated from Latin. Next to these texts, Ortelius also wrote popular or vernacular texts for all the Dutch, the 1572/1573 German and all the French atlas editions. These two types of texts were tuned to the audience for which they were intended: the Latin on verso texts and their derivatives aimed at an academic renaissance public that knew its classics. The popular or vernacular texts aimed at non-academics such as affluent merchants and civil servants. These atlases were among the most expensive but also among the most popular books of the 16th century. The texts which occur on some of the maps themselves never refer to the text on verso but the on verso texts refer continually to information on the map itself. The scholarly texts increased in size and information content with every new edition until Ortelius’ decease in 1598, while the vernacular texts hardly changed at all. The translations are well intended efforts to represent texts of the source language in the target language, but there are impediments: place names and personal names, particularly first names, were at the time translated as exonyms (Milano instead of Milan) and ‘exonames’ (Johannes, Jean, Jan, John, Giovanni etc.), which does not benefit transparence between languages. Ortelius was well aware of this disadvantage and on verso of his Low Countries map he provides a lengthy list of place names in as many as six different languages to prevent confusion. Moreover, differences between different language areas of a cultural, social or political nature often require a translation that is true to function, rather than to form. An inventory of all bibliographical sources mentioned by Ortelius in his on verso texts together constitute a part of Ortelius’ large personal library. This inventory shows that Ortelius had greatest confidence in his classical authors, less confidence in his contemporaries, and least confidence in medieval authors in terms of their reliability and credibility. The influence exerted by Ortelius’ on verso on his successors is diverse. For some cartographers, including his good friend Mercator, there was no influence at all. But other cartographers such as Hondius, Janssonius and the Blaeu family, correspondences are clearly evident, and sometimes entire paragraphs have been copied verbatim, (as were some of his maps). The conclusion of this study is that texts on verso of Ortelius’ atlas maps are of an innovative nature, and have been ignored for a long time without good reasons, for they present a vivid picture how Ortelius, a self-made encyclopaedic Renaissance scholar, experienced the world he lived in. Finally, Ortelius was also the first to popularise academic knowledge by fine-tuning his texts to the interests and mental grasp of his prospective readers.