I’ve been looking at Ptolemy’s information on the island of Britannia and have constructed a version of the southern part of England based on his coordinates. Whether it’s oriented correctly or whether it should be tilted slightly doesn’t matter for the moment. Some of his geographic locations (as far as they’ve been identified) are obviously wide of the mark; but, notwithstanding that there may have been a number of inaccuracies introduced between Ptolemy’s time and the late medieval copies that we have, some of it must have been at least what he intended – even if not necessarily accurate.
This is my rough (all right, very rough) map, with a few speculations, based on his latitude and longitudes:
And just for a bit of fun I took a modern map of the part of Somerset where Iscalis is likely to have been. Ptolemy’s latitudes for Bath (Aquae Calidae) and Iscalis are the same (53°40); and the longitude shows Iscalis somewhat to the east of Pumsaint (Luentinum), the former at 16*00, the latter at 15*45. So taking Ptolemy at his word, X marks the spot – the site of Iscalis, one of the key cities or towns of the Belgae:
However, I shall abandon that line of reasoning.
The black rectangle above is the area where I think Iscalis might have been. The top and bottom lines are, respectively, the rough latitudes of London (Londinium) and Winchester (Venta Belgarum), to the north and south of the latitude for Bath; and those to the left and right are the longitudes of Carmarthen (Maridunum) and Usk (Bullaeum/Burrium), which extend the western and eastern limits of the longitude of Pumsaint.
Within this rectangle, the two lower red dots mark the Roman ports at Combwich, where there was a ford across the river Parrett, and Crandon Bridge, a little further up the river. The area round the mouth of the Parrett is favoured by some scholars as a likely site. The other red dot is at the mouth of the river Axe whose name suggests a form similar to Isca, from a Celtic word meaning water – Isca Dumnoniorum was Exeter, on the river Exe.
All these four possibilities (well, three if we discount the middle of the Bristol Channel) are to the west of Charterhouse on Mendip (not Hinton Charterhouse – I got a bit mixed up), another important Roman site and centre for lead-mining in Roman times, which some have suggested. I’m going to rule it out for the moment as well as Cheddar, another important Roman site, because I had another idea. Which will follow.