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The comparison between the Carta Pisane (C1); Cortona Chart (C2); Vesconte Charts (C3); Riccardiana Chart (C4) and the Lucca Chart to a Geographical Mercator Chart is made possible by the regularising of their scale sizes using the North African coastline as the test.  Therefore, each chart is compared to the other by diagrams which illustrate the findings far better than the written word. But be careful of any tendency to view them and then over emphasis the contiguity of charts presented at a small scale. There is obviously greater visual disparity at a larger size chart presentation at which these were drawn, but one instance is nearly a precise match indicated by the diagrams and the finale.

Note; The Laurenziana Chart (C5) would have been included if the Biblioteca Medicea Laurenziana, Florence Italy, had responded to my request and it was found to be relevant.

Charts C6 to C10 are the subject of a second paper, ChCs/2, following shortly.


The North African coastline from Tangier to Alexandria is very accurately measured as exemplified by the “Itinerarium Antonini” with its distance measures for the coast road between those two cities. In my text ChLcP/1, “Les Cartes Portolanes” I indicated that this could be used to test chart distance measure and illustrated it with the Djerba Island to El Arisch distance (actually 2200KM). Thus this accuracy of known distance measure gave the charts and maps at their inception the high degree of distance accuracy we now observe.
The Church/Monastic community took great interest in Geographical matters from its earliest period. They copied  many Roman and Greek texts and itineraries and thus in my ChPo3, “Leather Vellum Parchment” text I opined that the original base map for these charts was probably produced in a Monastic/Church environment in northern Italy.  The Church/Monastic communities were driven by the requirement for knowledge; it being power. The knowledge they particularly craved was of the oikoumene, the known world and its extent. This can be readily observed from the text by Paulus Orosius, an Iberian cleric, who at the behest of St. Augustine of Hippo (-Regius = Annaba, Algeria, N Africa) commenced his Opus Maior with chapters 1 and 2 of Book 1, describing the geography of the oikoumene as my text CgPaO/1 illustrates.
Thus I consider the comparative distance chosen is correct for this examination and capable of being used to test the general Portolan portfolio for scale and accuracy.

I have compared each chart with all others noted, but not in sequential order. This is to enable an explanation of each in a logical manner rather than by rote. However I commence the examination of each chart noted with a comparison to the Geographical Mercator chart such that there is a base point which correlates across the whole investigation. I have chosen to use the number system from “Les Cartes Portolanes” merely to enable an order to be established and not enter into the Pujades/Campbell discussion of chart dating. I have written a very short note on that subject already: it is reference ‘ChCpo1’, “The Carta Pisane; Date Unknown”, and I hope sincerely in the interests of good research that the request made and noted there in will prompt the BnF to  respond to my written request for a Radio-Carbon Dating of the Carta Pisane promptly!
The individual diagrams are now discussed in few words; it is visual!



Carta Pisane (C1) -/- Geographical Mercator Chart.

Having aligned Djerba Island/El Arisch it will be readily observed that the length of the Mediterranean Sea from Tangier to El Arisch is compatible. The basic alignments of the Balearics, Corsica/Sardinia, Italy, Greece and Asia Minor correspond well to the geographical plot. It would therefore appear that the cartographer had good intelligence apropos the Mediterranean Sea basin, but that the partial western coastline of Iberia, France and north Europe was uncertain and probably an inspired guess. Unfortunately the Pontus Euxine/Black Sea area has been lost from the chart and thus a judgement on its overall presentation cannot be made. However this does show a high degree of draughtsmanship, belied by its state and as I have previously noted in my ChWr/1, “Wind Rose Construction” text the draughtsman obviously knew geometry and how to set out a wind rose (ChWr/2).


Carta Pisane (C1) -/- Anon Cortona Chart (C2)

There is a degree of visual correspondence between these two charts which hints at possibly a basic single original template, although that was perhaps from a copy of a copy, but it must also be noted that the divergences are quite marked. Unfortunately the missing section of the Cortona Chart tends to inhibit a real comparison and thus perhaps conclusions drawn previously by other researchers as to similarity of origination are not proven by this comparison.


Carta Pisane (C1) -/- Anon Riccardiana Chart (C4)

The correspondence in the western Mediterranean Sea and of the north coast of Africa is excellent, as is the positioning of Crete/Cyprus, the Peloponnese and Asia Minor’s western coastline. As the Riccardiana chart is a full Atlantic to Pontus Euxine Chart it will quite naturally offer greater possibility of conformity to all other charts, but the origination therefore of the Carta Pisane must be evaluated carefully to account for this possible visual correspondence.


Anon Cortona (C2) -/- Geographical Mercator

The eastern Mediterranean Sea covered by C2 is quite compatible with the Geographic Chart as is the position of Italy. A minor adjustment to the position of the north of Italy, keeping all other parts contiguous would produce a reasonably accurate chart. The over-exaggeration of the Pontus Euxine/Black Sea does not hide the basic accuracy of positioning apropos Asia Minor.


Anon Cortona (C2) -/- Anon Riccardiana (C4)

It is possible to opine that C2 is probably copied from the same basic template as C4; perhaps through a copy of a copy, but nevertheless with enough similarity remaining.


P Vesconte 1311 (C3) -/- Geographic Mercator

Here we see for the first time a chart which if the Geographical Mercator was not overlaid could acceptably pass for a “correct” chart of the eastern Mediterranean Sea. The northerly elevation of Italy/Corsica/Sardinia is as we have seen previously a regular feature of the comparison of a Portolan Chart and the Geographic Mercator Chart. However the close comparison of the Pontus Euxine/Black Sea profiles is particularly impressive.


P Vesconte 1311 (C3) -/- Carta Pisane Chart (C1)

What little we have shown on C3 of the western Mediterranean Sea area accords surprisingly well with C1, as does the N African coastline. Thereafter there is little to compare other than a good general east/west positioning of Greece, Crete, Cyprus and Asia Minor.


P Vesconte 1311 (C3) -/- Anon Cortona Chart (C2)

With a little westwards twist the Anon Cortona Chart would be seen as a reasonable alignment to the P Vesconte Chart. Certainly from a similar template, but the over large Sea of Azov on C2 may stem from the Carta Pisane template, but that is pure speculation.


P Vesconte 131 (C3) -/- Anon Lucca Chart

Yet again we see a western Mediterranean Sea or Ligurian/Tyrrhenian Sea alignment as well as the North African coastline. Typical features in the eastern Mediterranean Sea align but the Aegean Sea and hence the Pontus Euxine are badly out of position by comparison.

Diagram ChCs/1/D10

P Vesconte 1311 (C3) -/- Anon Riccardiana Chart (C4)

The correspondence between these two charts is quite remarkable and I will opine that they are in all probability either by the same hand or from the same Atelier or are copied from the same original chart template.


I find it quite strange that the extant Vesconte Charts commence with a chart of 1311 which is a quite accurate eastern Mediterranean Sea Portolan, but from 1313 we have only a series of Atlas. The fact that the Atlas could be drawn without the necessity for an overall Portolan chart being available for reference instilled serious doubt in my mind and led to the conclusion that we are probably missing a chart, c1300-1310, which would encompass the whole of Mediterranean Europe and be the guide for the drawing of the various Vesconte Atlas. The knowledge of the whole chart is required for the sections.

At this point in my investigation I consider that the Anon Riccardiana chart (C4) is in all probability a contender for that missing Vesconte Chart. If it is not actually proven a Vesconte Chart, then it and the template for the Vesconte Charts were from the same original and that original could possibly be the base chart from which all others eventually derive.
I have therefore included two atlas charts of Western Europe merely as visual examples of the type and then compared a singular Atlas Chart.


P Vesconte 1313 Atlas BnF Paris


P Vesconte 1318 Atlas Museo Correr Italy

These two charts are in fact comparable by scale as the one is twice the scale of the other. As the 1318 chart is the larger the detail is finer with the Atlantic coastline being well defined. Britannia has yet to attain a geographical outline. It should also be noted that these two Atlas charts are constructed as per the research in my “Wind Rose Construction” text.


P Vesconte 1325 Atlas -/- Anon Riccardiana Chart (C4)

Chosen for being perhaps the farthest removed of the Vesconte Charts from any possible linkage to the Anon Riccardiana chart which is possibly from the same Atelier, I have set the two charts with Africa and Iberia contiguous for a comparison to be made.
It would take but a minor adjustment westerly of France for an excellent correspondence between these two charts. Is this a minor draughtsmanship problem?


Anon Riccardiana (C4) -/- Geographical Mercator


Anon Riccardiana (C4) -/- Geographical Mercator

The length of the Mediterranean sea from the Pillars of Hercules to El Arisch is acceptable, as is the general positioning of the lands within the Mediterranean Sea basin, albeit with the northerly progress of the Italian Peninsula. The eastern Mediterranean Sea basin is accurate and the Pontus Euxine is very close to a Geographical representation.
The problems arise in the Atlantic and the western seaboard of Europe where Iberia and France are severely foreshortened, thus Britannia is misplaced.
However if this chart is to be dated to c1300-1310 (or earlier), it is quite remarkable.


Anon Riccardiana (C4) -/- Wind Graticule

One of the features of the P Vesconte Charts and Atlas is that the Wind Rose Graticule is drawn according to the trignometrical ratios of 35:30:20:7 units measured by the scale bar of the chart. As can be seen from the diagram the measurements are set out precisely as 35:30:20:7 from the Anon Riccardiana scale bar. Is this the base setting out?


Anon Lucca -/- Geographical Mercator


Anon Lucca -/- Geographical Mercator

Here again we see a good correspondence in the length of the Mediterranean Sea with general alignments in accord. The chart is drawn with a full wind rose graticule of the correct trignometrical units, 35:30:20:7 units.
The Iberian Peninsula is reasonably accurate in size although France has been severely curtailed in latitude (see above) perhaps to allow Britannia to be included, but unfortunately the 17th century reduction of the charts size has precluded a definitive statement. Whether the whole of Britannia and the Pontus Euxine would have been included is speculative, but with two very specific wind rose graticules set out on the chart it could well mean that there was not a great deal of actual chart removed by the cutting.


Anon Lucca Chart -/- Wind Rose Graticule

This diagram has been included as the partially extant scale bar appears to indicate that the Wind Rose Graticule has been set out to the standard 35:30:20:7 units as per the P Vesconte Charts using the scale bar as the measure.


Anon Lucca -/- Carta Pisane Chart (C1)


Anon Lucca -/- Carta Pisane Chart (C1)

These two charts have an excellent congruence for the Mediterranean Sea basin. Their lengths from the Pillars of Hercules to El Arisch are acceptable as is the entrance area position to the Pontus Euxine. The Aegean Sea is slightly awry in size and depiction of the Khalkidhiki Peninsula in the north is similarly awry.
The Iberian Peninsula on the Lucca Chart is quite acceptable: France is foreshortened and Britannia is indicated but there is disagreement between the two generally.


Anon Lucca -/- Anon Cortona Chart (C2)


Anon Lucca -/- Anon Cortona Chart (C2)

What little we have of the Cortona Chart shares a commonality with the Lucca Chart with the same distortions in the northern Aegean Sea as already discussed.


Anon Lucca -/- Anon Riccardiana Chart (C4)


Anon Lucca -/- Anon Riccardiana Chart (C4)

The general correspondence is excellent and follows a trend concerning the Anon Riccardiana chart (C4) in that it appears to be all things to all charts


It is however very easy to see concurrences or correspondences across charts which are perhaps fleeting in their actuality. However, there is in all probability at least one chart which is the template for all that follows. We may not be seeing the original but a copy of a copy, however we must consider the possibility that we have extant a master template chart.


Diagram ChCs/1/D21A & B comprises the whole range of the normal sailing routes of the Medieval period. Thus in the west is part of Britannia, the coast of Europe, the French and Iberian coasts to the Atlantic Ocean as well as south of the Pillars of Hercules part of the N African coastline, basically that of the old Roman Province of Tingitana Mauritania. The whole Mediterranean Sea basin and the Pontus Euxine/Black Sea with the Sea of Azov are included.
Given the size of the chart (c51 x 98cm) it is well endowed with toponyms for all the coastlines drawn. There are four scale bars which vary slightly in length and subdivision but this appears to be slack draughtsmanship and not alternate measures.
The horizontal centreline was drawn first, as can be seen by its continuation full length of the vellum. The chart was then lined out with a rectangular frame which was curtailed in the NE corner to allow for the Black Sea, and thus required a degree of pre-planning on the part of the draughtsman. However there does not appear to be any reason for the height restriction to the chart other than the actual measurement of the wind rose graticule. Hence at the Gulf of Sirte the toponyms are out with the frame: but it must be stated that all internal lines do stop at the framing and thus it was a first decision for size.

The frame size is therefore finite and is determined by the trignometrical ratios of the 22 ½ degree alignments, and hence it is 368 x 184 TRU’s or scale bar units. It would appear that the wind rose graticule set out to the 35:30:27 units required the 27 unit to be subdivided into the more normal 20 and 7 units, and this was achieved by using a pair of compasses and a short section of the wind rose circle in the north east corner of the western wind rose. I suspect that a pair of dividers would have been used to measure the required offset distance from the scale bar for the 7 units and the part circle is merely a cautious draughtsman’s check to confirm accuracy and show future users the methodology.
A careful visual inspection of the chart will indicate setting out lines across the wind rose graticule extended unnecessarily, and even an extra 45° line in the NE corner to determine the stopping points for the northern and eastern frame lines.
It would also appear it may not have been an entirely flat piece of vellum as in the SE quadrant the lines appear to meander, no doubt due to a twist in the surface. The errors are exaggerated east/west but contained north/south.

As there are limited holes for either the stretch frame or flat board fixing for the vellum, it has probably been cut to its final rectangular shape with near perfect perimeter measurement outside the charts frame.



They are lined out in traditional fashion with green major lines and red subsidiary lines all drawn from a black (?) line graticule. However, the central joint area is devoid of major lines as the diagram indicates and the general periphery has few lines. Thus this Portolan chart is probably easier to read than many which follow and have a multitude of unnecessary lines: {are we seeing later charts covered in more and more lines as “value for money” to impress clients as many of the lines are irrelevant}.
The second diagram has the scale bar (in green) set against the graticule lines of the 30 unit division and explores the continuation wind lines across the NE corner (Black Sea) with a reduced actual wind rose colour code drawn. The western wind rose is drawn normally.




A basic freehand plot of lines of Latitude and Longitude has been included to illustrate the general angular alignment of the chart to the graticule and Wind North. It also serves to illustrate the minor discrepancy in the alignment of Italy and Greece noted on several charts. The 36N latitude is fairly represented by wind rose alignments in green across both formers and if actually used as the 36N latitude it could account for the northern shift in the latitudes shown thereon.




The chart is of the eastern Mediterranean Sea from and including Corsica/Sardinia to the eastern littoral of the Black Sea. It is slightly longer than its height (42 x 52cm) and is framed similarly to the Riccardiana chart (see diagrams). My text ChWr/1, “Wind Rose Construction” explains its setting out. There are two exceptional features, the Danube and Dneiper estuaries which are highly coloured, but the Nile Delta, although shown properly appears to be of secondary importance.
The size of the chart (42 x 52cm) for its coverage compared to the Riccardiana chart (51 x 98cm) makes it a 5:4 ratio or 125% larger and hence there is greater coastal length for toponyms to be inserted. That raises a very large question which must now be discussed.


I have not been impressed by the arguments put forward that toponyms can be used per se to date and categorize Portolan charts. Firstly, as just illustrated, the actual scale of the chart that is compared by coastal lengths will determine just how many toponyms can be included there on. The argument of similarity of chart size when the list in pages 204/206 of Les Cartes Portolanes is studied is incorrect.  The main factor is how much of the Mediterranean Sea basin etc., is shown on a chart and thus how much larger is the actual scale and therefore coastal length for toponyms to be written.

Even the argument that a newly founded port/town included on a chart illustrates its dating is possibly fallacious. If the scale of the chart were such that the toponyms were spread out then there would be space to add a newly founded port/town toponym onto a chart which could have been drawn a decade earlier for its original drafting. Do we know how long a chart was held before a purchaser arrived, were they all pre-ordered , pre-sold with client requirements known for the decoration: I think not. Would a client not wish to see a sample or base chart?
Did all purchasers of charts require the latest data in all parts of their chart for the Atlantic/Mediterranean/Black sea areas if their main concern was for example only the Iberian/Corsica/Sardinia/Italian western Mediterranean trade area? Would they have known there was a new port/town that was not included in possibly the Black Sea area?

Yes I can readily agree nowadays we would require the latest data to be included as our use of a map or chart is probably so very different, but, was the primary concern of the 14th and 15th centuries for local traders, ship owners etc., the whole area or localised areas they used.
Professor Piero Falchetta in his 2007 paper, “The Use of Portolan Charts in European Navigation during the Middle Ages” (private copy from author) concluded as follows;

“To conclude, I would say that nautical treatises of the Middle Ages do not describe the use of Portolan charts in navigation at all because the whole matter was entirely determined by the practice of navigation. In other words, Portolan charts could be wrong in so many details that it was almost impossible to prescribe rules for their actual use before knowing the level of their relative exactness. Cotrugli, on the contrary, as a learned man accustomed to abstract concepts, was not interested in the practical use of Portolan charts. His treatise subsumed theoretical and practical knowledge within the same effort to render a general description of navigation.
As a consequence of these elements, the shape of the world in general and of Europe in particular, as it appears on the Portolan charts of the Middle Ages, is the result of a pictorial tradition which has very little to do with the concept we now have of maps as symbolic representation of space. The very fact that the Portolan charts continued to be composed in the traditional way even after “scientific” cartography had greatly developed- and the very fact that still at the end of the seventeenth century we have charts drawn in the same traditional manner they had been compiled three or four centuries before- suggests that the geographical model emerging from those maps was in a certain sense uninterested in establishing a technical relation with modern geography and scientific cartography. In conclusion, we can say that the image of Europe that we receive from thses Portolan charts reflects the anachronistic symbol of medieval nautical practice more than the image of a geographical space.”

Thus we can perceive that the charts perhaps not being used at sea for navigation purposes, but probably “library” charts need not be 100% accurate in the toponyms!
The Riccardiana chart has 48 toponyms for the northern Adriatic Sea area as listed by Pujades. His list indicates that the Vesconte chart has 52 toponyms, the 48 match each chart.

I think we must step back from supposed consensus, from the texts which appear to be so authorative and carry out a root and branch re-assessment. My texts and technical research  have shown that historians have missed so much that is important in the development of these Portolan charts, how they were drawn, their contiguity and their hidden assets and in the end indicates they have interpreted those charts wrongly in some instances. This is fully explained in my website text, ChLcP/1, “Les Cartes Portolanes, a critique of the technical sections”.



I have aligned the centre lines of the Riccardiana (C4) and Vesconte 1311 chart (C3) drawn at the same scale. Check the scale bars, they are also a matching measurement, and this reduction of the Vesconte chart comes not from the scale bars being aligned but the distance from Djerba Island to El Arisch being equal. Thus the scale bars align as proof of my theoretical stance.

Having shown they are in a 5:4 ratio, that is 125% and reduced the Vesconte chart, I have aligned the eastern portions of each chart which illustrates a similar setting out such that if the Riccardiana chart is the master, then the Vesconte chart is shown as a faithful copy even though it is enlarged by 125% in its final presentation: Excellent draughtsmanship!
Thus it is quite open for me to opine that they are both drawn from the same base chart.


By the 1200’s a very accurate map of the Mediterranean Sea basin and the Black Sea, plus all the peripheral lands existed. This was not a magnetically biased chart but a true map based no doubt upon countless measurements taken from 200BCE to 300CE by the Romans on land and at sea.
The church/monastic community were the inheritors of the Roman data and in their quest to “conquer” minds in the oikoumene for their religion they required to know its shape, distances and populations, as had the Romans with their world survey,.

Thus the geographical treatises were written and maps were drawn culminating in a visually accurate map being produced which we now see incorporated in the Portolan charts. The art of finding latitudes and the introduction of Longitudinal Tables undoubtedly helped. The length of a degree of latitude was accurately known by the Romans as 75mpm, and this combined with the Itinerary measures would have made map construction easier once coastline sketches were assembled. The fact that the degree measure was corrupted later is nonsensical and well documented.

Then a peculiarity arose: the magnetic Compass. Immediately there were two North Points; Geographical North determined by the course of the Sun through the heavens and a nebulous north point indicated by the magnetic floating shard of metal. But they both gave considerably different readings for north on the Iberian Peninsula and at Alexandria. When these charts are at their most formative the difference is a deviation of 16 degrees.

And yet researchers are wont to state that mariners did not know about magnetic declination. That pre-supposes a mariner could not rationalize the difference between the sun shadow line at midday showing true geographical north and a magnetic compass showing at Alexandria a 16 degree deviation. That is a 1 ½ wind deviation. I think otherwise!

But at all times the Portolan Charts have the Windrose graticule drawn and in most instances labelled to suit geographical north etc.

Then the map is twisted through normally 11 ¼ degrees to counter the deviation and ensure if all else is equal a course could be sailed by the compass direction. Thus the difference was rationalised and a method conceived to counter the difference, the chart.
When that took place is difficult to state, but in 1311 we have a very accurate chart which did not appear out of thin air. It had to be developed from at least from c1265CE when the magnetic compass was proposed, although Alexander Neckam wrote that it was known earlier.

Thus in all probability the Riccardiana chart, ms 3827, can be seen as the ultimate chart copied from a map by a Church/Monastic community, one which perceived the importance of the magnetic compass and had the technical ability to solve the enigma of two north points. This chart was then copied, possibly many times and became the template for many ateliers to produce their own versions. Thus we see in diagram D26 the excellent correspondence between the two charts when the North African littoral is equalised.
But of course, if as has been suggested these Portolan charts were not actually used at sea then their presentation is just a draughtsman’s idea of amalgamating the two north points and perhaps allowing a certain logical usage, however actually mistakenly, as the magnetic deviation could have caused chaotic mis-direction.

Carta Pisane; held by BnF Paris, Dept des Cartes et Plans, Res Ge B1118
Cortona Chart; held by Cortona Accademia Etrusca Italy, port 105
P Vesconte 1311 chart; held at Florence Italy, Archivio di Stato, CN1
Riccardiana chart; held by Biblioteca Riccardiana Florence Italy, ms 3827
Lucca Chart; held by Archivio di Stato, Lucca Italy. Fragmenta Codicum, Sala 40, cornice 194/I
P Vesconte; 1327, Florence Biblioteca Medicea Laurenziana , ms Med Pak 248
Itinerarium Antonini Augusti et Hierosolymitanum, edited by G Parthey and M Pinder, 1848.
Paulus Orosius, Historiae adversum paganos libri VII, Book 1, chapters 1 &2. The text is available in my cgPaO/1 website text, An analysis of Book 1, geographical text.
Pujades I Bataller, R J. 2007, Les Cartes Portolanes, Institut cartographic de Catalunya
Wright, J Kirtland, 1923, Notes on the Knowledge of Latitudes and Longitudes in the Middle Ages. ISIS, vol 5, No1, pp75/98.
Whyte Nicholas, 1991, Liber de Astronomice iudicandi. Roger of Hereford’s 12thC Astrologers Manual.
Petrus Peregrinus de Maricourt, Epistola de Magnete, letter dated 1269 translated 1904 available at

M J Ferrar May 2015.