Humboldt-Universität zu Berlin

Zusammenfassung

Composed in the city of Alexandria, one of the most prominent intellectual centres of the Roman Empire, Claudius Ptolemy’s Geography offers a description of the known world as well as insight into the practice of scholarly geography during the second century CE. Ptolemy’s most important innovation in this field was to use geographical coordinates to create maps of the world. His catalogue, in which the latitudes and longitudes of thousands of localities are listed, is one of our most valuable sources on the antique world.

Very little is known, though, about the sources and methods used by Ptolemy in producing his Geography. Moreover, the oldest Greek manuscripts of the work date from the end of the thirteenth century and supply two very different versions of the work. The Geography’s textual history from Ptolemy to the extant manuscripts is poorly documented. The starting point of the thesis has been to combine several fields of investigation – history of ancient sciences, textual history and textual criticism – in order to reconstruct Ptolemy’s sources and working methods. The thesis focuses on the chapters of the Geography devoted to the Iberian peninsula – his map of Iberia is certainly one of the most accomplished parts of the Geography.

The study shows that Ptolemy used a progressive, multistage procedure to determine the geographical coordinates. He neither measured longitudes and latitudes with on-site celestial observations nor calculated them. The coordinates are probably a result of geometrical constructions on a working map (using basic tools such as a ruler and a compass), combined with geographical information that he could easily have obtained from the literature available to him at the time. Localities were thus constructed and marked down as points on a map. Ptolemy read the coordinates directly from his map and recorded them in his catalogue. In many cases, it is possible to identify the sources of the geographical information: for example, the distances used by Ptolemy often closely resemble or are identical to other antique sources.

Using a classical philological approach on Ptolemy’s catalogue of Iberia shows that the two extant versions of the text have had very different histories. Moreover, the thesis argues one of the version – which has always been considered the less accurate one – is actually nearer to Ptolemy’s original text. The thesis postulates that Ptolemy structured and hierarchised the information of the catalogue in a way that would enable any cartographer to easily reproduce the maps. This element of Ptolemy’s practice enables us to set up new criteria for philologists to assess whether a coordinate in a manuscript is likely to be the original or has been corrupted during the transmission of the text. It allows us to reproduce his map of Iberia as accurately as possible.