Saxon Thegn

Ptolemy Geographia - decyphering Albion(Scotland)

Background

Ptolemy was an astronomer and mathematician who probably worked in Alexandria between 127AD and 148AD, he wrote a number of Astonomical, Mathematical and Astrological books, and his Geographica (about 150AD) that describes the locations of towns, tribes and rivers across the Empire.

This document shows a way to decipher and understand the logic of the latitude and longitude measurements given in Claudius Ptolemy’s Geographia for the Island of Hibernia which is modern day Ireland.

Many people have tried to understand this, but as far as I know no one has yet used the following method.

▼ My Hypothesis
▼ Ptolemy Data Format
▼ Analysis by other parties (Bill Thayer)
▼ Ptolemy Raw Data
▼ Plotting latitudes
▼ Plotting longitudes
▼ Theoretical map of Britain if Wexford and Bremen are used as the recording points
▼ Conclusion

My Hypothesis ▲

That the latitude and longitudes quoted in the Geographia are not true latitudes and longitudes, but are calculated from a few known fixed locations.

This would mean that the variation in shapes from the real modern maps can be explained, and hence Settlement locations that have not yet been identified can be shown on modern maps.

Ptolemy Data Format ▲

The first thing to notice about the Ptolemy data is that the decimal points after the main number go to a maximum of .55 so it would seem logical to assume that each East/West segment was divided into six. Hence a section between 58 and 59 North and 10 to 11 East would consist of a 6 x 6 matrix (36 individual points) to provide granular accuracy, and if the entry went to .05 would allow even finer granularity (144 individual points).

However it would also seem that if a whole number with no decimal places is shown for example 11 East, that it could either be along the 11 line, or somewhere between 11 and 12 implying that the accuracy was not as good.

Summary:
If a number is displayed with a .05 accuracy it would probably mean that they were more confident of the data, if .1 then less so and finally if both were whole numbers then even less so.

This would mean in turn that the locations we should assume are the most accurate are those containing .05 entries, followed by those with .1 finally whole numbers.

Analysis by other parties (Bill Thayer) ▲

There are a number of other people who have been interested in this subject and have tried analysing Ptolemy’s data with differing ways of plotting the variance between his data and current maps.

The very first of these modern plots that I have found in the early 2000’s was created by Bill Thayer in his massive LacusCurtius website, which I show below.

Map of Albion - Bill Thayer - LacusCurtius

Bill plotted a number of maps from the Geographia, but decided that they were not particularly productive as most show significant differences from the real world, implying that this was too time consuming and not very useful for others looking at this subject.

The theory was that Ptolemy plotted real world latitudes and longitudes and these could be directly mapped.

Ptolemy Raw Data ▲

The following are the locations quoted by Ptolemy for Albion, I have excluded those for Scotland as these appear to need a serparate analysis.

Please note: the red latitude longitude pairs are my suggested corrections after plotting on my last map.

A description of the northern coast, above which is the Duecaledonius ocean.
Novantarum peninsula, and promontory of the same name	21*00	61°40(Mull of Galloway)
Rerigonius bay	20*30	60°50(Loch ryan)
Vindogara bay	21*20	60°30(Irvine bay)
Clota estuary	22*15	59°20(Firth of Clyde)
Lemannonius bay	24*00	60°00(Near Prestwick)
Epidium promontory	23*00	60°40(Mull of Kintyre)
mouth of the Longus river	24*30	60°40(Loch Linnhe)
mouth of the Itis river	27*00	60°40(Loch Ewe)
Volas bay	29*00	60°30(Loch Eriboll)
mouth of the Navarus river	30*00	60°30(River naver)
Tarvedum or Orcas promontory	31*20	60°15(dunnet head)
Description of the west a side which borders on the Hibernian ocean and the Vergionius ocean.
From the Novantian promontory	21*00	61°40(Mull of Galloway)
mouth of the Abravannus river	19*20	61°00(Gillespie Burn)
Iena estuary	19*00	60°30(River Cree)
mouth of the Devas river	18*00	60°00(River Dee)
mouth of the Novius river	18*20	59°30(River Nith)
Ituna estuary	18*30	58°45(Solway Firth)
Moricambe estuary	17*30	58°20(morcambe bay)
Setantiorum harbor b	17*20	57°45(Skipool - Fleetwood)
Belisama estuary	17*30	57°20(river ribble)
Seteia estuary	17*00	57°00(river mersey)
Caeanganorum promontory	15*00	57°00(Great Orme)
mouth of the Toesobis river	15*40	56°20(Tremadog Bay)
mouth of the Stuccia river	15*20	55°30(Afon Dyfi)
mouth of the Tuerobis river	15*00	55°00(Afon Ystwyth)
Octapitarum promontory	14*20	54°30(St Davids Head)
mouth of the Tobius river	15*30	54°30(River Loughor)
mouth of the Ratostabius river	16*30	54°30(River Usk)
Sabrina estuary	17*20	54°30(River Severn)
Uxella estuary	16*00	53°30(River Axe)
Herculis promontory	14*00	52°45(Hartland point)
Antivestaeum or Bolerium promontory	11*30	52°30(Lands End)
Damnonium or Ocrium promontory	12*00	51°30(Lizard Point)
Description of the south side below which is the Britannic ocean. After the Ocrium promontory is
the mouth of the Cenio river	14*51	51°45(River Fal or Fowey)
mouth of the Tamarus river	15*40	52°10(River Tamar)
mouth of the Iscas river	17*40	52°20(River Exe)
mouth of the Alaunus river	17*40	52°40(River Axe)
Magnus Portus	19*00	53°00(Portchester)
mouth of the Trisantonis river	20*20	53°00(River Arun)
New harbor(Novus Portus)	21*00	53°30(Pevensey)
Cantium promontory	22*00	54°00(South Foreland)
A description of the eastern and the southern side next to which is the Germanic ocean. After the Tarvedum promontory, or Orcades, by which it is known,
Virvedrum promontory	31*00	60°00(Duncansby Head)
Verubium promontory	30*30	59°40(Noss Head)
mouth of the Ila river	30*00	59°40(River Helmsdale)
a high shore	29*00	59°40(Balintore)
Varar estuary	28*00 e	59°40(Beauly Firth)
mouth of the Loxa river	27*30	59°40(River Lossie)
Tuesis estuary	27*00	59°00(River Spey)
mouth of the Caelis river	27*00	58°45(River Deveron)
Taezalon promontory	27*30	58°30(Kinnairds Head)
mouth of the Deva river	26*00	58°30(River Dee)
mouth of the Tina river	24*00	58°30(River tay)
Boderia estuary	22*30	59°00(Firth of Forth)
mouth of the Alaunus river	21*20	58°30(River Aln)
mouth of the Vedra river	20*10	58°30(River Wear)
Dunum bay	20*15	57°30(Tees Bay)
Gabrantuicorum bay with many harbors	21*00	57°00(South of Flamborough head)
Ocelus promontory	21*15	56°40(near withernsea)
mouth of the Abi river	21*00	56°30(The Humber)
Metaris estuary	20*30	55°40(The Wash)
mouth of the Gariennus river	20*50	55°40(River Yare)
A promontory	21*15	55°05(Felixstowe)
mouth of the Sidumanis river	20*10	55°00(river colne)
Tamesa estuary	20*30	54°30(Thames)
Next to this the Cantium promontory	22*00	54°00(South Foreland)
The Novantae dwell on the side toward the north below the peninsula of this name, among whom are the following towns:
Locopibia	19*00	60°20(Mull of Galloway Promontory Fort)
Rerigonium	20*10	60°40(Stranraer)
Below are the Selgovae, among whom are the following towns:
Carbantorigum	19*00	59°30(Whithorn Promontary fort)
Uxellum	18*30	59°20(Glenrochar Roman Fort)
Corda	20*00	59°40(Corridoo)
Trimontium	19*00	59°00(Wardlaw Hillfort/font>)
From these toward the east, but more northerly, are the Damnoni, among whom are the following towns:
Colanica	20*45	59°10(Selkirk)
Vindogara	21*20	60°00(Avisyard Hill)
Coria	21*30	59°10(Carronbridge)
Alauna	22*45	59°50(Edinburgh)
Lindum	23*00	59°30(Bonnytown fort)
Victoria	23*30	59°00(Fast Castle)
Further south are the Otalini, among whom are the following towns:
Corstopitum	20*10	20*10(corbridge?)
Alauna	23*00	23*00(Learchild ?)
Bremenium	21*00	58°45(High Rochester)
Next to the Damnoni, but more toward the east near the Epidium promontory are the Epidi and next to these the Cerones; then the Carnonacae, and the Caereni but more toward the east; and in the extreme east dwell the Cornavi; from the Lemannonis bay as far as the Varar estuary are the Caledoni, and above these is the Caledonian forest, from which toward the east are the Decantae, and next to these the Lugi extending to the Cornavi boundary, and above the Lugi are the Smertae; below Caledonia are the Vacomagi, among whom are the following towns:
Bannatia	24*00	24*00(?)
Tamia	25*00	25*00(?)
Pinnata camp	27*15	59°20(Tayside)
Tuesis	26*45	26*45(?)
Below these toward the west are the Venicones, whose town is
Orrea	24*00	58°45(Carpow)
More toward the east are the Taezali
and the town Devana	26*00	59°00(Chester)
Below the Selgovae and Otalini f are the Brigantes extending to both seas, among whom are the following towns:
Epiacum	18*30	58°30(Whitley Castle)
Vinovium	17*45	58°00(Binchester)
Caturactonium	20*00	58°00(Catterick)
Calatum	19*00	19*00(?)
Isurium	20*00	57°40(Aldborough)
Rigodunum	18*00	18*00(?)
Olicana	19*00	19*00(?)
Eboracum, Legio VI Victrix	20*00	57°20(York)
Near which on the Opportunum bay are the Parisi and the town
Petuaria	20*40	56°40 g (Brough on Humber)
Below these are the Brigantes but some distance toward the west are the Ordovices, among whom are the towns:
Mediolanum	16*45	16*45(?)
Brannogenium	16*45	56°15(Leintwardine)
From these toward the east are the Cornavi, among whom are the towns:
Deva, Legio XX Victrix	17*30	56°45(Chester)
Viroconium	16*45	55°45(Wroxeter)
Next to these are the Coritani, among whom are the towns:
Lindum	18*40	56°30(Lincoln)
Ratae	18*00	55°30(Leicester)
Next are the Catuvellauni, among whom are the towns:
Salinae	20*45	20*45(?)
Urolanium	19*20	55°30(St Albans)
Next to these are the Iceni,
Farther eastward and near the estuary of the Tamesa are the Trinovantes
and the town Camulodunum	21*00	55°00(Colchester)
Below the peoples we have mentioned, but more toward the west are the Demetae, whose towns are:
Luentinum	15*45	55°10(Pumsaint)
Maridunum	15*30	54°40(Carmarthen)
More toward the east are the Silures
whose town is Bullaeum	16*50	55°00(Usk)
Next to these are the Dobuni,
and their town Corinium	18*00	54°10(Cirencester)
then the Atrebati
and their town Caleva	19*00	54°15(Silchester)
Next to these, but farther eastward, are the Canti among whom are the towns:
Londinium	20*00	54°00(London)
Daruernum	21*00	54°00(Canterbury)
Rutupie	21*45	54°00(Richborough)
Below the Atrebati and the Canti are the Regni and the town
Noeomagus	19*45	53°05(Chichester)
Below the Dobuni are the Belgae and the towns:
Iscalis	16*00	53°40(Dowsborough hill fort)
Aquae calidae	17*20	53°40(Bath)
Venta	18*40	53°00(Winchester)
Toward the west and south of these are the Durotriges whose town is
Dunium	18*00	52°40(Hods hill)
Next to these, but more to the west, are the Dumnoni, whose towns are:
Voliba	14*45	52°00(Castle an Dinas)
Uxella	15*00	52°45(Launceston)
Tamara	15*00	52°15(Plymouth)
Isca, where is located Legio II Augusta	17*30	52°45(Exeter)
The islands which are near Albion island and the Orcades promontory are:
Scetis island	32*40	60°45(Skye)
Eastward from the Trinovantes region there are two islands:
Below Magnus Portus is the island Vectis,
the middle of which is in	19*20	52°20(Blackwater)
Above these islands are the Orcades, about thirty in number,
the middle of which is in	30*00	61°40(Orkney)

Plotting latitudes ▲

Firstly I have coloured all the locations with the same latitude? in the same colour to try to find an originating point.

From the tracks of the latitudes? it would seem that these originate from the top of the coast in Denmark or possibly Aalborg. There is a possibility that this originating point could be the South of Sweden but this is much less likely.

It also looks like the northern islands are measured from Bergen, but there are few to be certain of this and they may just have been recorded incorrectly.

There are a few inconsistencies such as the islands on the west coast marked in red that must have a different origination point.

Plotting longitudes ▲

Firstly I have coloured all the locations with the same longitude? in the same colour to try to find an originating point.

From the tracks of the latitudes? it would seem that these originate from Northern France near Brest.

As you can see from the latitude numbers they are backwards, therefore my assumption is that the whole of Scotland has been rotated towards the right, how would this be possible ?

Let us now make a large assumption that if Scotland is rotated, then the two points that make the Scottish grid were plotted from incorrect points. The distance between Aalborg and Brest is about 1300 Km and that from Bremen to Wexford is just under 1100 Km so it is possible that Ptolemy made the assumption that the data from Brest originated in Wexford and the data from Aalborg originated in Bremen.

This in turn would imply that the data:

Was plotted from the wrong locations, i.e Wexford not Brest and Bremen not Aalborg
Wasn't Roman as they would have been more accurate and would have known the originating locations.
This in turn could imply that the data was from Pytheas who had travelled in this area about 330BC, but his stopping points were not known by Ptolemy, who assumed that his locations were the same as major Roman ports.

Let us assume the above statements are correct what would the map of Great Britain look like.

Theoretical map of Britain if Wexford and Bremen are used as the recording points ▲

Ptolemy Scotland if mapped from Wexford and Bremen

This map shows what happens if Scotland is mapped according to the Hibernia and Albion maps with latitudes from Wexford and the longitudes from Bremen. And the rest of the UK and Ireland mapped from Cadiz and Wexford.

It now looks similar to Bill Theyer's map albeit with more accurate data, so my assumption is that my theoretical locations the Romans used to map this area are close to the real ones.

It is possible that Bremen wasn't the eastern point but was around the end of the Limes near Nimagen, but this would scale Scotland down a bit

Conclusion ▲

I believe that the data for Hibernia and the South of England were measured from Cadiz.

The northern part of England and Wales were plotted using Wexford and the Inchitutil Fort in Scotland(or more likely its harbour at Bertha).

Finally that the plot of Scotland was created using Pytheas data, but with the incorrect assumtions that the two points he had referenced were Wexford in Eire and Bremen in Germany.

If all the above assumptions are true, then we can deduce that Pytheas most likely travelled from Marseille to Cadiz the Brest and up to Aalborg before sailing round Scotland and probably up to Iceland.