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Claudius Ptolemaeus was a Roman citizen of Macedonian descent (Rivet & Smith 1979, p.103), living and working in Alexandria, Egypt in the second quarter of the first century A.D., and wrote all his scientific works in Greek. His work,  like so many ancient others (especially those in the Library at Alexandria), was lost for over a thousand years to Western scholarship. It was not until the 15th century that his work was rediscovered and translated into Latin, the commonly used language of western scholars at the time.  

Ptolemy was a geographer, mathematician, astronomer and poet, whose works resonated for many centuries. There are three of his surviving works that have historical significance,  the Almagest (the Great Treatise) on mathematics, the Tetrabiblos (four Books) about philosophy and astronomy, and Geographia, the work that concerns us here. The Almagest contains observations made up to A.D. 141 and at the end of its second book Ptolemy promised a fuller work on geography; we can therefore confidently date the Geographia to between A.D. 141 and c.150, although much of the material is clearly derived from earlier writers (ibid.). In his Geography, Ptolemy described and compiled all knowledge about the world’s geography in the Roman empire of the mid 2nd century, an enormous undertaking.

As with all of the classical works that have come down to us, Geography was copied and re-copied by hand many times, and during this process errors of transmission crept in. In addition, many of his maps were not redrawn when the work was copied and so the copies we have today are either missing maps altogethe, or only contain medieval versions based upon his descriptions. The omission of maps from works like this was already recognised as a problem as early as AD 956, by al-Mas’udi, an Arabian scholar, although he was almost certainly talking about a different geographer, possibly Marinus (Berggren & Jones 2000, p.48). Indeed, not a single contemporary map of Britain comes down to us, making Ptolemy’s work invaluable.

The work consists of eight books, the first being an introduction which is highly critical of Marinus of Tyre, his principal source. He also explains his general principles, and the theory of map projection. The next six books deal with the then known world one province or country at a time, and are essentially lists of peoples and places along with latitude and longitude. The British section is in Book II, and includes various tribes and peoples who lived here, the towns and cities within their territories, along with rivers, estuaries, coastal features. Ptolemy’s method of plotting one place in relation to another was to use the bearing and the distance along it, although it is also clear that he utilised maps that had been plotted by others before him.  Latitude was measured horizontally from the equator while longitude was measured from the westernmost landmass known at that time, the Canary Islands off of the coast of Spain. It is fair to say, however, that the accuracy of many of the coordinate pairs is not great, and there are serious issues with his methods of projection, caused in part by his acceptance of an inaccurate estimate of the earth’s circumference (Rivet & Smith 1979, p.106).

His sources seems to have been aware of some of the surveying involved in road planning, for example he remarks in criticism of Marinus of Tyre “and having said that Noviomagus [Chichester] is 59 miles further south than Londinium [London], he then shows it further north in Latitude.” (Geography I, 15, 7). London and Chichester are 59 miles apart as the crow flies, not by measurement along Stane Street (RR15), and the alignment of the northern part of Stane Street along the direct bearing is very well known. It would be a very useful exercise to extract from his work any similar long distance alignments which he utilised. This would certainly enlighten our understanding of Roman surveying and road planning although, as far as we are aware, this has not yet been attempted. In any case, his use of such cross-country measurement may be the exception rather than the rule, as most of the distances between places (calculated from his coordinates) are wildly inaccurate.  

One well known issue with the British Section of his work is the “turning” of Scotland (see Fig. 2), which appears to have been caused by Ptolemy obtaining his information on Scotland from a map which hadn’t been correctly aligned north-south, rather than from a list of co-ordinates. This can be demonstrated by the solution to the issue, which simply involves rotating the map of Scotland anticlockwise about 1/7th of a circle (not 90 degrees as is often stated) in relation to England and Wales, using the mouth of the R. Eden as the pivot (Rivet & Smith 1979, p.114).

Until recently, there had been no satisfactory English translation of the Geography, the previous one by E.L. Stevenson being generally regarded as, in Bill Thayer’s words “abysmally bad”. There are now two, one available only in hard copy by Berggren & Jones (Berggren & Jones 2000), and the other online, by Louis Francis (Francis 1994).  Stevenson’s translation is also available online from Bill Thayer, and in an easily readable presentation of the British section on the Roman-Britain website.

Berggren, J. Lennart  & Jones, Alexander (2000); Ptolemy's Geography: An Annotated Translation of the Theoretical Chapters; Princeton University Press, Princeton & Woodstock

Francis, Louis (1994); Ptolemy’s Geographia Books I & II; accessed 22/9/17

Rivet, A.L.F. & Smith, Colin (1979); The Place-names of Roman Britain; B.T. Batsford Ltd., London

Fig. 1. A rendering of Ptolemy’s Geography, printed in 1482, by Donnus Nicholas Germanus

© Richard J A Talbert & Cambridge University Press, 2010


The Antonine Itinerary De situ Britanniae - an 18th Century Hoax The Peutinger Table The Ravenna Cosmography Ptolemy's Geography The Notitia Dignitatum

Fig. 2. A map projection of Britain and Ireland from an edition of Ptolemy’s Geography published in 1467 at Reichenbach Monastery, showing the peculiar distortion of Scotland