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Within Les Cartes Portolanes, pp511/512 there is a continuous dialogue concerning the Carta Pisane (LCP C1) and Cortona Charts. Many of the points raised there-in require to be further discussed and others clarified to present an up to date view of the Cortona Chart. Thus the “LCP” text will be used as a framework for the first section of this research.
“Les Cartes Portolanes, page 511: Portolans and Portolan Charts: from the Compilation of Information to its Graphic Representation”.
“An old hypothesis that has been repeatedly defended by some authors and rejected by others contends that charts are merely the result of transferring information on distances and directions, previously systematised in portolans, to a graphic format64. Nonetheless, in recent years the idea has come to prevail that the first nautical charts emerged at the moment when people began to compile and fit together partial maps of the different basins that constitute the Mediterranean, which ship’s officers had begun to do at an earlier stage65. But while from the viewpoint of the 20th and 21st centuries that might seem to be the most likely option, I believe it is difficult to uphold.

The first and most obvious problem the theory poses is that it assumes that this kind of map actually existed. So that medieval mariners might have put together the partial maps of the different basins that comprised the Mediterranean – which it is assumed they did on board the vessels that sailed each sector of the coast -, this type of map would have had to circulate with relative frequency, thereby making it possible to copy, purchase or exchange maps of different sections until a picture of at least a substantial part of the Mediterranean coastline could be drawn. However, no reliable traces, either direct or indirect exist that would support the arguments of those who defend the theory.
64 = the idea had already been defended by Kretschmer and was taken up again by Lanman with new arguments.
65 = the idea was put forward by Nordenskiold, and, combined with the support of portolans, also by Kretschmer.”


“The oldest extant partial chart, Vesconte’s from 1311, is a work covering over half the Mediterranean and clearly based on the model of a global chart; consequently it fails to serve even as a late example of the above mentioned assumed kind of map67.” (A chart noted as Mappaemundi of at least the whole Mediterranean Sea)
67 = Florence, Archivio di Stato, CN1. (LCP, C3)
“And the difference in scales of the representations of the Black Sea and the Atlantic coasts, recently pointed out by Kelley and Messenburg, confirms what we might easily deduce from the logic of events, namely that these two areas were incorporated later (in accordance with their later inclusion in the major trade routes) into the original representation of the Mediterranean68.
68 = Kelley J E, The Oldest Portolan Chart;&, Messenburg P, Numerische und Graphische Analysen zur Geometrischen Struktur von Portolankarten.”
Having set the parameters with the above we can commence an examination of the Cortona Chart and its differing scale bars, as shown on diagram ChCOR/1/D01. The main scale bar is set in a circle near the centre of the chart and is somewhat traditional in its layout covering 200 Millara on a vertical format. To the north is a very different scale bar; some 283mm in length it is incomplete being only partially subdivided. It is obviously a work in progress for the chart. If the two scale bars are examined side by side then it becomes obvious they have a simple relationship of 6:5 units; that is 6 units of the central design equals 5 units of the northern scale bar. I have already opined in text ChMAT/1 that the Millara is based upon the Roman Mile or Mpm and is 5/6ths of the Mpm, probably the resultant of the 60,000 uncia (and 80,000 digitus) subdivision of the Mpm, being reduced to 50,000, as has happened elsewhere. Thus the Mpm of 1.4791Km becomes the Millara of 1.232592Km, and 50,000 uncia. But, it is also the Miglio of the medieval Italian states and cities. As will be clearly shown the central scale bar is for the Mediterranean Sea area and the “incomplete” scale bar is for the Black Sea area only. Thus we have two areas with differing scales; why is another mystery to be solved.But why were they used on the Cortona Chart and the one not completed?


The first point to be considered is did the draughtsman just take an” LCN” quoted set of distances for the Black Sea and draw them as Roman Miles and not Millara, hence a 20% expansion in size. Or, did he have a text which quoted Millara figures that had been labelled as Roman Miles hence he would have automatically converted them to Millara by increasing them from 5 to 6 units or the 20%: this must be acknowledged as the simplest of errors for a scribe to make. Note how in “Liber” it is “ml xxx” for distances and LCN uses millara. The one can be easily mis-read for the other, similar to the Roman numeral problem of 50 and 100 being L and C, but mistakenly read. That indicates that there could have been a text available to the draughtsman which detailed the Starea distances using a differing annotation, but only for the Pontus Euxine. In that instance he would draw a Roman Mile scale bar.
The first proposition is hard to evaluate; why would a draughtsman suddenly change the scale from one used for the whole of the Mediterranean Sea area, the Millara, and use the Roman Mile for the Pontus Euxine? That makes no logical sense at all.


But the second is logical as the draughtsman having drawn the Pontus Euxine, noted it was perhaps oversized, checked the distances and realised it was drawn to the wrong scale following the wrong notation of the distance measure. Hence a new scale bar had to be appended. But at this point in the proceedings the draughtsman halted with an unfinished scale bar, then probably scrapped the chart, cut sections off for use elsewhere and then allowed the whole to be used as a vehicle for a text on the reverse, which did not rely upon the usage of the Pontus Euxine section of the drawn chart.


Written in Gothic Chancery Script are some 169 lines of text, difficult to read in many places but set at an equal distance from the edges of the mutilated parchment. It appears to be a religious itinerary of the Holy land and indicates distances between Egyptian and Palestinian towns noted for pilgrim routing. It also discusses the Nile flooding and its origin. In the middle there is a sketch of two saints; one seated the other standing around whose head is the name “St do-minicus”. In addition there are some numbers written in very small lettering, mostly illegible, but by a different hand.
Return to the chart and the Pontus Euxine area and there under three place names, G de Ladiri; G de Sinopi and G de Cimisso, are minutely written words which appear to be an annotation for the actual places. The G de Ladari is adjacent to the River Partengo (LCN), Parthenius (Arrian) and the Parteni of the chart and corresponds to the River Billeaus or Filyus River. The G de Sinopi is obviously the large gulf to the east of Sinope and the G de Commisso is west of Ciminio, Summaros or Amisus now Samsun.
Thus it is open to speculate that this chart is a copy of an earlier chart and has been marked out for guidance in an area perhaps not well known to the later cartographer. Indeed a previous researcher, V Armignacco, has indicated it as a possibility writing as follows;
“The text is Italian shown by a certain usage of the terminology. Palaeographers consider the text to be before the 14th century. It is a copy made in Cortona from an older chart shown by the poor representation of the Sea of Azov which is correctly shown on charts of the early 14th century, although the chart by Giovanni de Carignano does slightly agree”.
Did the copyist just make a mistake and thus use the chart for another reason?



In my text ChMAT/1, I indicated the usage of LCN Millara distance measures within the Cortona Chart for the Mediterranean Sea itself but avoided any mention of the Pontus Euxine/ Black sea which occupies the north east corner of the chart for obvious reasons.
Simply put, from the Bosphorus the whole of the Pontus Euxine is drawn using the Roman Mile or Mpm scale bar shown to the north of the chart and west of that sea. Thus it is drawn 20% or 5:6 ratio larger than the Mediterranean scale and the consequence is visible. But LCN details the Mare Maiore, Black Sea in millara for its Starea section; there is only one distance measure which could be considered a Peleio. However the “Liber” text is annotated in miles within which there are only around 100 such distances. The Cortona Chart has 111 toponyms and they accord only sporadically to the LCN text, and thus it could be opined, as already noted, that the LCN text used for the Mediterranean Sea area did not include the Mare Maiore and thus a second text was required to complete the chart, which was misread for distances.
It is now necessary to return to LCP, page 511 for a continuance of the storyline;
“The incorporation of the Atlantic coasts needs no particular comments on my part: it is enough to examine the Carta Pisane and the output from the Vesconte and Dulceti ateliers in chronological order to verify how quickly their design evolved from a hard to recognise diagram to a reasonably more identifiable outline69. The case of the Black Sea since it was incorporated during the 13th century and the section of the Carta Pisane where it appears has come down to us seriously deteriorated, cannot be analysed so visually, although neither does this pose a serious problem. If we compare the description of it in Liber de existencia riveriarum (dating from shortly after the time [1204] when the sea was opened to western navigation)70 with the one provided by the Conpasso de Navegare ( the definitive version of which dates from the last years of the 13th century, that is, after the foundation of the Genoese colony of Caffa {present day Feodosiya})71, the evolution is also easily perceivable as opposed to the detail with which the Compasso describes the Bosphorus and the coasts near Constantinople, the Liber passes quickly over this region, restricting itself to sketching out a number of crossings, in the vast majority of which the space devoted to indicating the distance in miles is left blank. Furthermore, the Compasso, having completed its description of the Mediterranean, states quite clearly that one unit comes to a close here and proceeds to describe another, called the Mare Maiore de Romania, also in detail (which is not without its significance in terms of what I am attempting to explain here)72.
Now that I have clarified this point, the differences in scale between the Mediterranean basin, the Atlantic and the Black Sea which invariably appear in 14th century charts, far from serving to support the hypothesis according to which nautical charts were formed from the juxtaposition of partial maps, becomes a solid argument against it: the evenness of the scale within the Mediterranean basin (with the usual variations I commented on above) and its clear difference from those of the Atlantic and the Black Sea indicate that the initial was drafted in one piece, while the peripheral areas were added subsequently, coinciding with their later incorporation into the major medieval maritime trade routes.”

The above text should be qualified by the actual text within P G Dalche’s book, “Liber”, page 8, as follows;” A l’autre extremite de la mer interieure, les toponymes du Pont ne sont guere nombreux, non plus que les indications de distance, tres souvent laissees en blanc, ce qui semble temoigner d’une faible frequentation des commercants europeens, plus faible en tout cas qu’au XIII siècle. La seule place importante connue d’ailleurs est Soldaia de Crimee (Soudak, Soldadia liber), mais il n’est pas fait mention de Caffa ni de la Tana, don’t on connait l’importance au XIII siècle.33
33 = Idrisi ne mentionne pas non plus Caffa, don’t la foundation date vraisemblablement de 1266 ou peu après ( M Balard, La Romanie genoise, XII debut du XV siècle, t. I,Paris, 1978, p117)”

Unfortunately it appears that Caffa started life as Theodosia, as named by Arrian in his “Periplus Pontus Euxine” and noted as deserted. It was originally a Milesian colony, and he states it is named in a number of texts. It is now Feodosiya and thus we may consider it was always known of and the deserted idea is not entirely true. It has been continuously occupied even after being “destroyed” in the 4th century, when it was occupied by the Golden Horde and called Keffe. If it was known in the Graeco-Roman times and as can be shown these older names have been carried through on both Portolan Charts and in the Portolani, perhaps our 20th century ideas of what should be, must be revised. However it is pertinent to note that it was not a Genoese city until 1266, being Venetian earlier from 1204 until 1261 when Genoa purchased it from the ruling Golden Horde and continued their name as Caffa. Why therefore should LCN not use Caffa, and why must “Liber” use it? But, it is pertinent to note that the Cortona chart has the following toponyms from east to west across the Crimea; Cavari- Zinue- Salaiuda- P Cafa- P Solcati – Saldaia. Thus we read of a Puncta Cafa, and not an inhabited town or port, and we do not read of Theodosia/Caffa.
The next point I do not agree with is the emphasis placed upon the completion of one section of “Lo Conpasso de Navegare” and the next, vis a vis moving from the Mediterranean Sea area to the “Mare Maiore de Romania”. They are not conjoined in a major manner, any more than the Atlantic Ocean is conjoined to the Mediterranean Sea. Thus for the author to state I have finished the one, described the coasts and then the major and minor islands, and will now describe the next is a natural progression of descriptive writing for these coastlines. Thus this is not a reason to consider that a change of map scale would be required.
To suddenly change a map scale for a single part of a Portolan Chart requires that there must have been an all persuasive reason or there was separate data available for each section and the draughtsman was unable to convert the one to match the other. The text within the extant copy of “Liber de Existencia” as stated by P G Dalche, and readily observed in the text, section 16, lines 955 to 1009, has no distance measures (or very few) which could have been used. That is not to reject an earlier or better version being available for the composition of the map of the Mare Maiore, but that point also applies to “LCN”.
Thus I consider that we must look to a much earlier period in the history of Black Sea exploration to explain how so much data was available to the various “Portolani” authors if access was limited until after 1204AD. The obvious text to be noted as the possible original is that of “Arrian, Periplus Pontus Euxine”, which is in effect a “Portolani” detailing the coastline by distance measures. It was written in Greek, uses the Stade for measurement, which are very easily converted to Roman Miles or Mpm and has 130 places noted. The correspondence of place names between “LCN” and “Arrian” is quite good and thus it is possible to opine they may be linked. The correlation between” LCN” and the Cortona Chart names is however less and as only 64 out of 111 chart toponyms are actual places, with 22 being capes; 12 are Puncta; 7 are Golfo, with 4 rivers and 1 Torre, it is perhaps not surprising.
However, if diagram ChCOR/1/D03 is studied which has both Cortona and a Geographical Black Sea drawn as overlay is studied, the accuracy can be observed. The two plots align at the Bosphorus with the geographical plot having been twisted such that the northern coastline of Turkey/Asia Minor aligns. Thus it can be shown that in the past a full survey of the Pontus Euxine took place and that data was readily available to the “LCN” compiler, but, could it have been completed between 1204 and 1261 when Venice held sway as after that the Byzantine forces recaptured Constantinople. Thus the text is most likely to have been written prior to the 4th Crusade and the Venetian capture of Constantinople in 1204. Bearing in mind also they already had three trade colonies, Sinope, Trapezus and Soldaia within the Black Sea and were trade partners of Constantinople which made the 4th crusade such a horrible event. The “Liber” could therefore be a basic outline copy of what was to follow, or an incomplete copy of an original completed text.


Within “Arrian’s” text, para’s 29 and 30 we read of the Palus-Meotide, the Sea of Azov, including of the River Tanais, the Don, the great river which since ancient times has been the boundary between Europe and Asia. (I use the French translation from the Greek).
29; “De Sindique au port appele Cimmerien et a Panticapee, ville du Bosphore, cinq cent quarante; de la an fleuve Tanais, qui separe, dit-on, L’Europe de L’Asie, soixante. Le Tanais sort du Palus-Meotide, et se jette dans le Pont-Euxin. Eschyle cependant, dans le “Promethee-Delivre”, fait du Phase la limite de L’Europe et de L’Asie. Les Titans, en effet, dissent chez lui a Promethee, “Nous venons, o Promethee! Pour voir tes souffrances et tes maux dans les fers!”. Puis, ils enumerent les pays qu’ils ont traverses: “La le Phase, grande et commune limite de L’Europe et de L’Asie”. On rapport que le tour du Palus-Meotide lui-meme est d’environ neuf mille stades.
30;”De Panticapee au bourg Cazeca, assis sur la mer, quatre cent vingt stades; de Cazeca a Theodosia, vill deserte, deux cent quatre-vingts; c’etait une ancienne ville grecque ionienne, colonie de Milet; et il en est fait mention de nombreux ecrits. De la au port desert des Tauroscythes, deux cents stades; de la a Lampas la Taurique, six cents stades: de Lampas au port Symbolon Taurique lui aussi, cinq cent vingt stades; et de la a la Chersonese Taurique, cent quatre-vingts. De la Chersonese a Cercinites, six cents stades, at de Cercinites au port Calos, Scythe lui aussi, sept cents.
This text is as good as the “LCN” and covers the whole area, was available to the “Church”, and could have been copiously copied as an addition to the Roman Itineraries. Thus we have a basis for the whole structure of an original “LCN” text. We must also not forget the “Tabula Peutingeriana” (see later) which has a complete circuit of the Pontus Euxine, with the Roman Road shown for Asia Minor, but also a closed Palus-Meotide, Sea of Azov.
Thus I conclude the increase to the scale for the Pontus Euxine was an error from copying a “Portolani”, which itself had been mis-copied regarding the distance measures.
The following text is taken directly from ChMAT/1, which is an examination of the Mediterranean Sea area of the Cortona Chart. The diagrams are included as the original text.


Being a chart with little history in textual terms it falls to draughtsmanship and mathematical analysis to uncover the basic facts concerning the chart; indeed I have found only one major paper regarding this chart. Although clearly reduced in physical size it would have been a typical Mediterranean Sea basin map with overall scope from Cape St Vincent to the eastern coastline of the Black Sea, some 9W to 42E longitude. In the south there are remnants of the Gulf of Sirte, thus it is latitudinally 30N to the Sea of Azov at 48N. It has two Windrose circles, the junction of which may be fairly described as the 15E longitude. The eastern circle is complete and extends to 35E. Curiously it has a centre line from East to West which could be considered the Gozomalta to Acre alignment. We can thus speculate that the western circle is from 15E to 5W, perhaps the Pillars of Hercules. It is also possible to speculate that the circles were drawn after the chart was prepared and they were thus positioned to suit the “LCN” text, (which I have already noted as a possibility on the Carta Pisane chart), thus following the east/west alignment from Acre to Gozocreti to Gozomalta would be a simple matter, but it is not true east/west, that is San Piero to Grapparola!


There are two possible scale bars set upon the chart. The central circular design is divided into 5×20 and 2×50 millara segments set vertically in the design. The second scale bar is across the north of the chart and a different matter entirely. By measurement it has a relationship to the circular scale such that c17 of the northern units is equivalent to c14 units of the circular scale. Thus we have possibly a simple 6:5 ratio of the scale bars. I have already opined that the millara is 5/6ths of a Roman Mile of 1.47911Km and is thus c1.23 Km nominally. Therefore we can establish from the Cortona scale bars confirmation of that relationship as well as being able to opine that the northern scale bar is none other than a scale of Roman Miles (mpm). It has been suggested that the derivation of the Millara is from the Roman Pes unit of 12 uncia, making the basic unit of measure 10 uncia or 5/6ths of a Pes. I do not subscribe to this theory as the measurement is too small to be of any use at sea and thus requires being a large multiple that can be easily established and measured when sailing.
BUT, I should also state that in Sicily and Italy in the Medieval period there were measurements, Miglio, which were virtually identical to the Roman Mile of 1479.1 metres.
At Palermo, the Miglio was 1487 metres, comprising 45 Corde or 720 Canne or 5760 Palmi.
At Genoa and Albengo, the Miglio was 1488 metres, comprising 1000 Passi or 6000 Palmi.
Thus the principal Miglio for road and sea distances throughout Italy, Sicily and Sradinia was based upon the Roman Mile, which was originally 8 Stadii (furlongs) of 1000 geometrical paces totalling 5000 feet, but by the later Middle Ages many variants had arisen because of the fragmentation of Italy into separate states etc.


Firstly, a comparison to “LCN” distance measures will establish if the Cortona Chart is compatible thereto and determine a basic accuracy for the chart. The four diagrams all have drawn thereon “LCN” alignments from the Peleio section and also have “LCN” chart and geographical distances noted. But from the very commencement of the research it became apparent that the Cortona chart was in one major instance using not only different Peleio distances, but by either deliberate action or serendipitous actions the errors which exist south of Sardinia had been corrected. The correction is partially made by using different geographical distance measures south of Sardinia compared to the extant “LCN”, but also that the overall length of Sardinia is increased by 35 millara to partially mitigate any “LCN” shortfall in the distances. Sardinia itself is N/S 215 millara but the chart has 250 millara, hence we record 690 millara along the 9E longitude where actually it is only 660 millara. But if we tabulate the distances, those given in “LCN”, as drawn on the Chart and the Geographical distances we can observe the accuracy and the chart differences.

San Piero to Boczea; CCCXX 310 (-) 310 (-)
San Piero to Bona; CLX 160 (-) 210 (-50)
San Piero to Galeta; C 125 (+25) 150 (+25)
San Piero to Bizerta; CXL 185 (+45) 200 (-15)
Taulara to Bona; CLX 150 (-10) 193 (-43)
Carbonara to Bizerta; CXX 170 (+50) 160 (-10)
Carbonara to Cape Bon; CLXX 205 (+35) 210 (-5)


Hence the chart plot from Genoa via Corsica/Sardinia, Galeta to N Africa is drawn as 690 millara when the geographical distance is 660 millara and akin to F Beccari trying to correct the same error within his 1403 chart and increasing the distance by 50 millara.
However, if we look at distances to ascertain the overall accuracy of the Cortona Chart it proves very accurate indeed. Thus from Aigues Morte/Menorca/Zaffone, total distance drawn is 600 millara, the geographical distance. I have already indicated the 9E distance as 690 millara on the chart and 660 millara geographically, but from Civita Vecchia to Tripoli in Barbaria is 1050Km, 854 millara; the chart is 850 millara. Also from Castello Roso to Alexandria; chart and geographical distance are equal at 450 millara.


The east/west measurements are on the diagrams and exhibit the same degree of accuracy. Thus the Cortona chart with its deliberate or otherwise alteration to the length of Sardinia which negates the other LCN errors does not produce a twisted or skewed chart, but a near geographical chart as the two diagrams with the graticule of longitude and latitude will clearly show. Thus up to and including the 38N line they are consistent. Then from 39/40 to 43/44 they all increase to cope with the enlarged Sardinia as is now discussed.


The geographical test is simply that Capo Corso is 43N and thus an excellent locating point, but, more importantly by projecting it westwards the 43N also denotes the Iles D’Hyeres and is the situation on the Cortona Chart. Thus below 38N we have consistent latitudes which vary as they cross the Ionian Sea to the Peloponnese, and below 36N an accurate chart again. The longitudinal lines are however set 6 degrees east to the putative 36N latitude, but are consistent across the chart. A general calculation indicates a 33:40 ratio longitude to latitude which equates to a latitudinal centre line of c35N. But remember, the ratio for 36N has always been thought of as 4:5 in antiquity and that equates to 32:40, so very close.
But as I have already opined, it is the distance measures, probably set out from Genoa, 9 East via the Peleio, which determine the putative ratio which were originally measured on the surface of the globe and thus should reflect the actuality of the geographical ratio.

ChMAT/1/D05 & ChMAT/1/D06

The basic conclusion regarding the Cortona Chart is therefore that it is a highly accurate chart, which either by luck or judgement has a draughtsman who has either corrected the “LCN” discrepancies which mar the standard Portolan Chart, or had another copy of “LCN” which displayed the more correct distances involved. The distortion is obviated and thus the reasoning for magnetic deviation does not exist on this chart, as with others investigated.
Would that it was a full chart, it may have held even more surprises!


That concludes the original ChMAT/1 text regarding the Cortona Chart, but it must be plainly stated that the accuracy I speak of there-in ignores the fact that the chart is skewed and is purely based upon the fact that the putative geographical graticule can be shown as reasonably correct. The following text obviously has greater detail but does not change that fact, nor remove the visual clarity it shows.



I have already opined that the error in draughtsmanship for the Black Sea scale when compared to the Mediterranean Sea scale was caused by the mis-reading or mis-labelling of distances by the use of “ml” which is the Miglio and not “millara”. Thus the one was substituted for the other and the 20% enlargement occurred.
Therefore it is also reasonable to opine that the draughtsman did not realise just how accurate the Mediterranean Sea area actually was on his chart; or did he?
There could be a second reason for the mutilation of the chart, that of certain knowledge the Iberian Peninsula and Atlantic coasts were wrongly drawn and when the error of the Black Sea scale was discovered, for why else would the scale bar be incomplete, the chart was mutilated, the offending portion removed, but the Black Sea problem accepted as inconsequential for the intended use of the chart, not for sailing, but for the Pilgrim route information written on the reverse to be visual as well as textual.
If as has been opined it is a copy of an earlier chart then the above scenario is quite acceptable and must also be a cautionary tale as to the intended use of charts.
However, if we assess the Black Sea as drawn the first problem with its positioning is shown by the overlarge latitudinal measurement of Asia Minor. It should be drawn as diagram ChCOR/1/D04 indicates; that is 120 millara less in latitudinal spread. That alone introduces a 15 degree twist to its alignment as the chart clearly shows.


But if as diagram ChCOR/1/D05 illustrates we try to align the Black Sea correctly there is the automatic twist of the putative longitudinal lines to those which can be drawn upon the main chart area and are counter-aligned to the putative latitudinal lines the previous diagram ChCOR/1/D04 illustrated. Thus it is necessary to remove the distortions from the Cortona Chart to realise the correct alignments for latitude and longitude.


ChCOR/1/D06 & ChCOR/1/D07

A comparison of the geographical distances to the Chart distances (given in Millara) indicates quite simply the raison d’être for the apparent mis-drawing of the Mediterranean Sea vis a vis the geographical plot. It is unfortunate that the western section of the chart has been removed as I believe that section would have indicated the first error in distance measure and thus the beginnings of the charts distortion.
Therefore we can only commence at the first natural alignment the chart affords us, which is from Aigues Morte via Menorca to Zazon (Zaffone), and is to all intents and purposes a north/south alignment. Draw that line on the Cortona Chart as diagrams ChCOR/1/D06 and ChCOR/1/D07 indicate and immediately there is agreement with not only the alignment from Algiers to Cape Bon, that being east/west and set at 90 degrees to the Aigues Morte/Zazon line, but if the putative 36N latitude is drawn also, then that is parallel to the Algiers/Cape Bon alignment. I have always used the Genoa to N Africa 9E longitude as a chart marker, but in this instance it is not parallel to the other alignment. The reason is very simple to determine and solve the mis-alignment problem. The distance from Aigues Morte to Genoa scales 384 Millara, but is actually only 317 Millara. Thus if the correct distance is marked from Aigues Morte towards Genoa on the alignment and that point is used to draw the new putative 9E longitude it parallels the Aigues Morte/Zazon line and is therefore of course set at 90 degrees to the two east west alignments, particularly the 36N latitude.
Such a tiny error on the chart is the main reason that there is a skewing to the north east of the Cortona Chart. This skewing produces a 4 Degree latitudinal error in the positioning of Acre, which coupled with the large error, 120 Millara, in the positioning of the Black Sea south coastline exacerbates the twist both actually and visually.



It is possible to indicate, by re-aligning the two sections of the chart, the Mediterranean Sea area and the Black Sea area just how easy it would have been for this chart to be spectacularly accurate.
But, as I have opined on many occasions the Wind Rose is the key to the whole chart. In my texts ChWR/1 and ChWR/2, I showed conclusively that Wind Rose were always drawn and considered to be geographically correct; that is they reflect the true orientation of NSEW, and thus the true wind directions and are not distorted in anyway. If the Cortona Chart is redrawn as an overlay to the original as diagram ChCOR/1/D08 illustrates with the Aigues Morte and Genoa north/south alignments and thus the 36N latitude correct, by pivoting the chart at Aigues Morte, it is immediately clear that the “new geographical overlay” repositions the Mediterranean Sea to a near perfect geographical alignment. The City of Acre moves 4 degrees south to its correct position and the NSEW of the Wind Rose align perfectly to the charts NSEW.
However, if the Black Sea area is dragged south as drawn, there is a mis-alignment. But if the correct distance from the 35N latitude on Crete to the 40N latitude at the mouth of the Dardanelles, the Bocca de Avedo, is drawn, .i.e. reduce the distance from 521 to 450 Millara and Sinope is again correctly positioned, as diagram ChCOR/1/D08 illustrates, a very acceptable map appears. It is overlarge in the Black Sea area by virtue of the 20% scale change, but nevertheless an acceptable geographically visual chart map.


The Cortona Chart is drawn from data obtained from within an “LCN” text and the coastal form taken from that texts accompanying small scale map. Thus when the matrix for the Cortona Chart was marked out on the vellum, before the coastlines were drawn, the locator points as diagrams ChCOR/1/D06 and ChCOR/1/D07 indicated, serious errors occurred in the actual scaling of distances and thus the chart distortion was the result.
The Black Sea is an enigma; its scale is obviously not that of the Mediterranean Sea area and as indicated within “LCN” from Constantinople it is a separate, self contained Sea area and most probably had a Roman Mile or Miglio (ml) distance measure which was taken to be a Millara by the charts draughtsman.
Thus there is no magnetic deviation within the charts construct and the inherent accuracy is a tribute to that draughtsperson and the “Portolani” plus its chart he used.
The following text in essay form is a discussion solely on the Pontus Euxine.

ChBLS/1; The Black Sea Enigma; Essay.

Following on from ChCOR/1 and the discussion vis a vis the differing scale bars, one for the Mediterranean Sea area, Millara; one for the Black Sea area, Roman Miles or Medieval Miglio, both of which are practically identical in length, it is necessary to confirm the distance measure used on the Portolan Charts for the longitude of the Black Sea.

Black Sea Geographical


The Black sea has been a nautical highway for millennia. From the 8th century BCE the Greek nation states or Cities had a number of colonies there, and specific trade routes from the north to south and east to west including sailing into the Palus Maeotis, Sea of Azov, to Tanais. Between the 8th and 3rd centuries BCE there were approximately 50 such colonies around the coastline.
Then the Roman Empire expanded, absorbing the Greek colonies and by the time Arrian wrote “Periplus Pontus Euxine”, wherein he quotes some 130 places with their inter-distances given in Stadia/Furlongs of c185 metres, the Pontus Euxine was a well known Sea.
Thus we can be certain that the actual knowledge of the Pontus Euxine was considerable with its longitudinal and latitudinal distances quite definitely known.

The Tabula Peutingeriana


I have included a copy of the excellent reproduction of the 4th century tabula which shows the Pontus Euxine with its road system and coastal towns. The Palus Maeotis is shown as a closed Sea with place names redolent of the medieval charts. If this tabula, the Itinerarium Antonini Augusti and Arrian’s Periplus Pontus Euxine are utilized distance measures can be quantified for the coastline of the Mare Maiore de Romania.

Black Sea, Medieval period

There is a paucity of itinerary texts from the medieval period, full stop!
We have; Liber de Existencia; Lo Conpasso de Navegare and Grazia Pauli. A fragment of another text is extant and in the USA, Minnesota, a text comprising 80 pages which have not been made available for study. (I and others have requested it!)
Thus the only text available to us which will permit a basic map to be drawn is Lo Conpasso de Navegare (LCN). This text has been shown to have numerous scribal errors of copying for both distances and directions, but surprisingly the text for the Mare Maiore de Romania section, folios 101 to 106 is perhaps the most original in that the errors are quantifiable and quite minor.


Having drawn the plot which derives from LCN distance and wind directions, it is possible to simply measure the longitudinal distance of the Mare Maiore de Romania to provide a comparison not only to the geographical distance but also to the various Portolan Charts and Atlases which clearly show that sea.
The distance as measured from the LCN plot is 1070 millara west/east as indicated, and compares to the geographical distance of 927 millara as an expansion of 115%, or a 15:13 ratio which can be reduced to 5:4.33 or 5: 5.77, close but not close enough to be considered the 6: 5 ratio of Millara to Roman Mile/Miglio.
But at least we now have a basis from which to carry out a comparative study.

Comparing LCN to Geographical and Cortona Chart

It is first necessary to state clearly that the LCN plot and the two comparative plots are not using precisely the same scale for the individual diagrams. Why? I am not trying to compare exactly the coastlines as the scales used are too small and given the Portolan Chart methodology of drawing scalloped coasts not actual coastlines, it is nonsensical to do that. I am using these plots merely as a visual guide to the general form of the Mare Maiore, thus enabling readers to assess the general accuracy of the profile rather than concentrate on minute detail (which I believe to be an irrelevance in the circumstances of these charts).



The first diagram, ChBLS/1/D04 compares the LCN plot to a geographical plot, but in order to overlay the geographical plot onto the LCN plot it has been twisted to the north-east by c11 degrees. As I have already shown within the main ChCOR/1 text this is due to the latitudinal measures of Asia Minor being c120% greater than reality. There is the obvious discrepancy regarding the northern inlet sea to the River Borysthenes which may or may not be an error. This is because of the split in the LCN descriptive text, ponente and levante and thus the junction of the two sections in this area may be hiding a scribal error of omission.
However, when diagram ChBLS/1/D05 is studied it becomes quite obvious that an LCN text was used to draw the Mare Maiore, but what has happened to the Palus Meotide, Sea of Azov is another unsolved enigma.

Comparisons of Chart Distances



The first diagram has appended four charts; LCP C3, C4, C6 and C7, which exhibit a variety of drawn longitudinal distances for the Mare Maiore. The charts vary thus; 1020, 1030, 1080 and 1090 millara, basically in accordance with the LCN distance, but, at variance to the geographical distance of 927 millara.
The second diagram has appended four more charts; LCP C7(2), C8, C9 and C19 and these have distances of 1058, 1084, 1030 and 1084 millara.
Therefore none are actually as overlong as the Cortona Chart, a 120% expansion.

Three Atlases, 14th, 15th and 16th centuries


The first Atlas used for comparison is LCP A9 dated to the 2nd quarter of the 14th century and is held by BNF, ms lat 4850. The Black sea is drawn 1150 millara/960 Miglio longitudinally which is the basic 120% expansion of 1.23Km to 1.4791Km already noted.
The second Atlas is by Andrea Bianco, Atlante Nautico, 1436 and has a drawn length of 1015 millara, which is a 109% expansion and thus could be ignored, considered correct.
The third Atlas is Joan Martines, 1578, and indicates precisely the same problems with the longitudinal measure of the Mare Maiore and the latitudinal measures of Asia Minor as found on the Cortona Chart. The Mediterranean Sea area is drawn to a correct millara scale and thus perhaps Joan Martines was not as informed as the draughtsman of the Cortona chart and did not realise the expansion error within his Atlas.


Concluding comments for the essay

The foregoing research confirms the facts already stated that there was a copy or copies of “LCN” which were inadvertently noted as “ml” and thus taken as miglio instead of millara. Thus the Mare Maiore has been increased by the 6:5 ratio of the measures, or 120%.
Whether the “ml” was an actual Roman Mile or the medieval equivalent of a Miglio, as there is only 8 or 9 metres difference is uncertain. But, as the Miglio is derived from the Roman Mile and as I believe the original “Alpha Chart” and “Alpha Text” were taken from Roman Itineraries and maps, it matters little if it is called a Roman Mile or Miglio.


But it leads me to the final conclusion that there were many copies of an “LCN” text which were accompanied by a very reasonable small scale coastal map to enable the various draughtsmen to draw their Portolan Charts and which therefore have such an amazing similarity. Basically they are one and the same. I believe that there was also a form of “gazetteer” available listing the ports which were not necessarily shown on the original “Alpha Chart”. Thus it could be updated over the centuries to include the latest ports. Thus the draughtsmen had an armoury of data for their intended Portolan Charts.
But please remember, Draughtsmanship before history will solve much more!!

M J Ferrar March 2016.