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Notes on Ptolemy’s Geography

Raw notes blog

This blog is a repository for my notes on historical topics, based on source texts of various kinds including primary sources and modern secondary works. It may not be all that readable, but will help me keep track of these sources which I may wish to refer to elsewhere. Much of it is connected to 17th and 18th century research I'm doing for my Substack newsletter Diamond Pitt.

However, I also have an interest in earlier history and in particular the development and transmission of knowledge about the world, in the form of ideas, inventions, beliefs and practices, from the early centuries of the Common Era onwards. My starting point is Ptolemy’s Geography, a landmark text from the mid-second century CE.

Claudius Ptolemy

Claudius Ptolemy (c. 100 CE – c. 180 CE) was an Alexandrian, and despite his name probably not related either to the Claudian or to the Ptolemaic dynasty. Nobody can be quite sure, as his personal history is obscure. He is best known for his two works in Greek, the Geography and Almagest. The Almagest is about astronomy (and astrology too – they were not clearly separated then). Geography, on the other hand, was an instruction manual for drawing maps of the world.

The most useful modern edition of Ptolemy's Geography is by Berggren & Jones in 2000 (see below). They have translated the theoretical chapters, which form a coherent treatise on constructing world maps and are separate from the more difficult to reconstruct tabular data that forms the bulk of the book.

The work’s Greek title, Geographike Hyphegesis, can be rendered as ‘Guide to Drawing a World Map’. B&J

Unfortunately this work has suffered poorly in the preservation of its text, partly because of the technical nature of its contents, which made it especially hard to copy accurately. All the available manuscripts (about 50 in number) can be shown to descend from a single ancestor, which may itself have been copied at an early date but already contains errors that show it was not the author’s original. Such is the way with studying ancient texts. Luckily, B&J have managed to find ways to retrieve a lot of sense out of the slightly messy raw material.

Through most of the Middle Ages, Ptolemy’s Geography was a rare and little-read text, a situation paralleled in the history of other ancient scientific and technical works. p.43

Ptolemy represented the culmination of a tradition of Greek thought which brought together mathematical, astronomical and geographical knowledge. By Greek, remember that as used in this context it means culturally Greek, not an inhabitant of the part of the world we know today as Greece. As noted he lived in what is now Egypt. The mainly Greek-speaking part of the Roman empire encompassed the whole of the eastern Mediterranean as well as much of north Africa.

The Greeks had learned about astronomical observation and mathematical techniques from the Babylonians, Egyptians and others, but more persistently than any before them they pursued the research goal of conceptualising and mapping the globe. Ptolemy’s final achievement covered 180 degrees of longitude and 80 degrees of latitude (between 20° S and 60° N).

He introduced the practice of writing down the coordinates of latitude and longitude for every feature drawn on a world map, so that someone else possessing only the text of the Geography could reproduce Ptolemy’s map at any time, in whole or in part, and at any scale. He was apparently also the first to devise sophisticated map projections with a view to giving the visual impression of the earth’s curvature while at the same time preserving to a limited extent the relative distances between various localities. p.3

Ptolemy’s work remained state of the art until the time of Columbus – who relied on his unfortunate under-estimate of the size of the Earth, and thereby hoped to reach China easily via the westward route. Ptolemy began from the state of knowledge available to him in his own Mediterranean milieu, principally the Greek-language tradition. In India also there is evidence of an early understanding of the spherical nature of Earth, and of occasional communication between these two regions. Evidence on this topic from other parts of the world is more sparse, but I will return to that topic another time.

Ptolemy’s geography rests explicitly on his conception of cosmology – theories about the shape and structure of the universe beyond our earthly habitation. The standard model in Greek thought was the nested-sphere model, in which the spherical Earth sits at the centre of a much larger sphere containing the stars. Following precursors in Plato and earlier writers, this theory in its detailed form originates mainly with Aristotle.

The entire sphere of stars, all imagined as being equidistant from Earth, rotated over a period of twenty-four hours. The movements of the planets (plus the Sun and Moon) took place above the Earth but closer than the celestial sphere. Their motions were very complicated, and remained contested, but luckily need not be considered in the context of the Geography. Ptolemy’s other major work, Almagest, describes his planetary theories, which remained standard until the work of Copernicus and Kepler.

This approach to cosmology, even though it may be (and was) used to underpin astrological readings, is essentially mechanical rather than mythological, a matter more of geometry than of spirituality. It represents one way of approaching the world, an observational and metrical approach. Thus one kind of view of the ‘known world’ was arrived, consisting of maps and star charts, combined with other scholarly works such as ethno-geographical treatises on the regions known to be inhabited and that had been visited by travellers.

There were also different cosmic theories of a more mythological character. Some, especially the Gnostics and neo-Platonists, drew upon the spherical model in their schemes of door-keepers and secret passwords to enable the rising soul to reach higher realms. Others such as the Jewish apocalyptic tradition and the Manichaeans employed a more conceptual notion of other worlds, not necessarily clearly defined in their spatial relation to our own. As well as the very technical approach of Ptolemy I intend to explore some of the more imaginative cosmologies of the period.

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