[NB. Place-name identifications indicated below are all explained in Chapters 10-16, which deal with Romano-British place-names in different regions of Britain.]
Chapter 18
Errors in the Geography of Ptolemy
1 It is evident that Scotland caused Ptolemy some difficulty. So much so that he turned the country through 90° so that it ran east-west rather than north-south. There are those who believe that this was because Ptolemy shared a belief common at the time that human habitation was not possible beyond the latitude 60° north. If this were true it would reveal a very unscientific mind, since a scientist, unless he had good reason to believe that the evidence he was being given, in the form of geographical co-ordinates, was unreliable, would modify his theory to fit the evidence. He would not modify the evidence to suit the theory.
2 But there is a clear error in the order of names in Ptolemy’s coastal list which can surely be ascribed to Ptolemy himself. He placed the Tuesis estuary and the mouth of the (Is)caelis river between the mouth of the Loxa river (the Lossie) and the Taezalon promontory (somewhere on the coast of Buchan), whereas in fact the Tuesis estuary was the Firth of Tay and the (Is)caelis river was the river now called the South Esk. Tuessis was the name of the Roman fort now called Bertha and the Romans simply transferred the name to the river, now called the Tay. The Firth of Tay was thus of course called the Tuessis estuary (by the Romans). And (Is)caelis was the name of the Roman fortlet at Inverquharity. Again the Romans simply transferred the name to the river, though at some stage of copying the initial Is of the name was lost. Presumably Ptolemy received his information from two different sources, the first listing the Tuesis estuary, the mouth of the (Is)caelis river and the Taezalon promontory in a south-north direction, and the other listing the Taezalon promontory, the mouth of the Deva river and the mouth of the Tina river in a north-south direction. Ptolemy wasn’t quite sure how to combine these names in one single list and simply assumed, wrongly, that the Tuesis estuary and the mouth of the (Is)caelis river were between the mouth of the Loxa river and the Taezalon promontory.
3 But Ptolemy’s error, discussed in the previous paragraph, caused some medieval copyist, who clearly had access to the Ravenna Cosmography, to commit an error. That copyist noted the similarity between Ptolemy’s river names Tuesis and Deva and Ravenna’s place-names Tuessis and Devoni, Devoni being the third name after Tuessis in the Ravenna list. He then assumed, trusting that the order of names in Ptolemy was in fact correct, that Tuessis was on the river Tuesis and that Devoni was on the river Deva. He then inserted Tuessis (changed very slightly to Tuesis) and Devoni (changed to Devana) in the Geography of Ptolemy and gave them co-ordinates to suit their assumed locations. And for good measure he also gave to Ptolemy’s Pinnata Castra, corresponding to Pinnatis, the name immediately before Tuessis in Ravenna, co-ordinates suitable for its assumed location a little to the west of Tuesis. There is no reason to believe that that medieval copyist acted other than in good faith. For reasons best known to himself he wanted to fill in an empty space in Ptolemy’s Scotland and was misled by the error in the order of names in Ptolemy’s coastal list.
4 There is also an error in the names Ptolemy assigns to the Selgovae – Carbantorigum, Uxellum, Corda and Trimontium - and here again the error appears to have been committed by a medieval copyist who had access to the Ravenna Cosmography. The group of Ravenna names after Maia Fanococidi, assumed to have been at Bowness-on-Solway, includes Carbantium, Tadoriton, Uxela, Corda and Trimuntium in that order. The copyist was aware that Ravenna had already listed names in the north of England, and knowing that Trimuntium was in Scotland (or perhaps Trimontium was actually in the Geography of Ptolemy), simply assumed, like countless scholars after him, that all of the names in that Ravenna group were the names of places in southern Scotland. One needs to remember that Ptolemy did not produce a map in the normal sense of the term – he produced a list of names, and the names in his list for the Selgovae appear in exactly the same order in the Ravenna list. One can thus see that Ptolemy’s Carbantorigum was not in fact a place-name at all – it was a simple conflation of the two adjacent Ravenna names Carbantium and Tadoriton. These two names have been run together to produce Carbantoritum, and it is this false name which has come down to us as Ptolemy’s Carbantorigum. (As explained in Chapter 15: Roman place-names in the North of England, the original form of Carbantium must have been Carbandium and that of Tadoriton probably either Cartadoriton or Cardadoriton - this might make the conflation of the two Ravenna names easier to understand). And it is clear that Ptolemy’s Uxellum corresponds to Ravenna’s Uxela at Chesterfield and his Corda to Ravenna’s Corda at Leicester. Trimuntium comes after Corda in the Ravenna list. Whether Ptolemy was right in assigning Trimontium to the Selgovae is open to debate, but what is not open to debate is that his co-ordinates for Trimontium are simply wrong – they place Trimontium near the inner end of the Solway Firth, the area thought to have been occupied by the Selgovae, whereas there can be no doubt whatsoever that it was at Newstead on the river Tweed.
[This page was last modified on 12 January 2021]