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The Medieval and Early Modern Nautical Chart: Birth, Evolution and Use

Periodic Reporting for period 2 - MEDEA-CHART (The Medieval and Early Modern Nautical Chart: Birth, Evolution and Use)

Reporting period: 2018-12-01 to 2020-05-31

The main purpose of project Medea-Chart is to solve a series of historiographical questions that have eluded the historians of cartography for a very long time, concerning the birth, technical evolution and use of old nautical charts. Such purpose is to be accomplished using innovative techniques – cartometric analysis, numerical modelling and the physical examination of the manuscripts under special lighting – in complement of the traditional methods of historical research. With the introduction of these techniques we intend, not only to solve some long-standing problems, but also to revitalize the discipline by opening new and exciting opportunities for research and training a new generation of historians prepared to apply consistently the new techniques to the study of old maps and charts.
Of all the technical and scientific developments that made possible the maritime expansion and early modern globalization, the nautical chart is perhaps the least studied and understood. Old nautical charts were not only indispensable tools for the mariners but also sources of geographical information in a time when the world was being discovered, explored and mapped by the European. Although the history of cartography is now a well-established academic discipline and old charts have been examined for many years, their function as instruments for navigation was never addressed in any systematic way, as most historians have focused their attention to the geographical, cultural, artistic or historical aspects, leaving behind the technical components. This is mainly explained by the fact that late-medieval and early-modern nautical charts are complex artefacts which can only be understood in the context of the contemporaneous navigational practises. That is why this intimate connection must be taking into account for the understanding on how those charts were constructed, how they were used by pilots at sea and how they contributed to change the world at a time when the size and shape of the Earth suddenly acquired a growing and critical relevance. Its is amazing to realize that those charts, which were constructed by uneducated pilots and cartographers, and did not even consider the sphericity of the Earth, were used to explore and represent the world for more than five centuries, before being replaced by the Mercator projection The explanation is that the full adoption of the Mercator project in navigation only became possible when the longitude problem was solved and the spatial distribution of magnetic declination was known, well into the eighteenth century.
Some of the historiographical issues that we want to clarify are:

- When, where and why were the first nautical charts of the Mediterranean produced? Although there is presently some consensus that the earliest charts were made around 1200 in Italy, following the introduction of the marine compass, the supporting evidence is still scarce. Furthermore, the results of our research suggest that primitive nautical charts not based on compass directions might already exist in the twelfth century, if not earlier.
- How were those charts constructed? There is a broad consensus among historians that the earliest charts were drawn using compass directions and estimated distance collected by pilots at sea. But the details of the construction process are mostly unknown. For example, it is uncertain whether the first model was constructed as a single cartographic unit covering the whole Mediterranean and Black Sea or as a piecewise assemblage of regional representations.
- How and when were the first charts based on observed latitudes constructed? We know that the earliest charts based on astronomical observations were introduced by the Portuguese, in the last decades of the fifteenth century. But the details and the protagonist of that transition are poorly known.
- How were nautical charts used at sea? No medieval or early modern texts have survived explaining in detail how pilots used
The research work performed since June 2017 has proceeded along four main general tasks, according to planning: the origin and evolution of portolan charts, the origin and evolution of latitude charts and the use of charts at sea.

Concerning the origin and evolution of portolan charts, a sample of about forty exemplars was chosen as to be representative of their overall geometry and technical evolution. Some were already examined using cartometric techniques, including the Carte Pisane (c.1290) the Avignon chart (c.1310) Mecià de Viladestes (1413), Angelino Dulcetti (1339) and Jorge de Aguiar (1492). The work done so far confirms a major hypothesis of the project, that medieval nautical charts were constructed using navigational data collected by pilots at sea, consisting in compass directions and estimated distances between ports. By correlating the spatial distribution of magnetic declination in the Mediterranean Sea during the Middle Ages with the geometry of the oldest extant charts, it was possible to conclude that the first portolan charts, the ones from which all the other derived, were probably made around 1200. The results of cartometric analysis further suggest that those charts were probably constructed as a piecewise assemblage of regional representations.

In collaboration with the French National Library, the Carte Pisane was subjected to a multi-spectral analysis, aiming to unveil hidden graphical content and clarify whether the chart is a palimpsest or not. This last point is crucial to refine the radiocarbon dating determined in 2017 for the parchment (1190-1290). The results will be made public during the Medea-Chart workshop of June 2020, in Lisbon.
A study of the Latin manuscript “Liber de existencia riveriarum et forma maris nostris Mediterranei” (c. 1200) was made, which included a new translation and interpretation of the Prologue and a quantitative analysis of the navigational data. Two important conclusions were drawn: that some form of primitive nautical chart not based on compass directions was used in its preparation; and that two distinct groups of directions co-exist in the manuscript: those measured with a primitive type of marine compass and those obtained by observation of the Sun and stars.

Concerning the origin and evolution of latitude charts, four Portuguese charts were studied and examined using cartometric techniques: the anonymous chart of the beginning of the sixteenth century known as Kunstmann III (now lost), re-dated as of 1501-1506 and now considered as the oldest extant latitude chart; the Atlantic chart of Pedro Reinel, previously dated as of c.1504 and now re-dated as of c.1519; the anonymous portolan chart of c.1510 known as Dijon chart; and the anonymous chart of c.1585 attributed to Luís Teixeira, the earliest known to depict lines of constant magnetic declination.

Research has proceeded around broader issues concerning the nature, limitations and functions of nautical cartography in the early modern period. Studies were completed about the intimate connection between pre-Mercator nautical charts and marine navigation, their intrinsic geometrical incompatibility with geographical maps, and how these issues generated misunderstanding and conflict among scholars, cartographers and pilots in the sixteenth century.
Concerning the use of early modern charts at sea, a commented anthology of texts included in contemporaneous navigational treatises and manuals, where the subject is discussed, is being prepared.

A relational database designed by the Medea-Chart team, with images and information about old nautical charts and atlases, is being developed. A preliminary version has already been disclosed over the Internet: https://medea.fc.ul.pt/main.
Most of the results of Medea-Chart’s research are original and add to the present state of the art. The same applies to the application of novel techniques to the study of manuscript charts, such as cartometric analysis, numerical modelling and multi-spectral analysis. The following achievements should be emphasized owing to their significance:

- The new pieces of evidence obtained from cartometric analysis in favour of the medieval origin of portolan charts, as instruments for navigation constructed with compass directions and estimated distances measured by pilots at sea (Fig. 1);
- The new pieces of evidence obtained from cartometric analysis in support of the hypothesis that the earliest portolan charts were constructed as a piecewise assemblage of regional representations (Fig. 2);
- The conclusions drawn from the study of the Liber de existencia riverierarum about the probable existence of a primitive model of nautical chart, not based on compass directions and preceding the one of Carte Pisane;
- The new interpretations about the geometry and nature of pre-Mercator nautical charts as instruments for navigation;
- The new interpretations made around the differences between maps and charts in the early modern period, and how they were the cause for misunderstanding and conflict between the various protagonists using them;
- The evidence produced from the study of the anonymous Portuguese chart known as Kunstmann III that it was probably started around 1501 and incorporates observed latitudes for the northwester coast of Africa. This makes Kunstmann III the oldest known latitude chart (Fig. 3).
- The development of a database developed by the Medea-Chart team, with information and digital images of old nautical charts, atlases, authors and archives, now freely available over the Internet (Fig. 4).


During the next two and half years, research will proceed along the lines defined in the project description. Concerning medieval nautical cartography, other charts will be studied using cartometric techniques, namely the ones showing signs of cartographic improvement or significant geometrical deviations from the norm. The close examination of local geometric features and its correlation with magnetic declination spatial distribution will continue, in order to investigate the details of chart construction and try to identify the regional parts which may have been used to construct the earliest charts. A broader and promising approach to the origin of nautical cartography issue is now under development in the scope of a doctoral research, which includes the identification of the actual maritime routes used in the two centuries prior to the first portolan charts, the distribution of knowledge across mariners, and the use of the modern concept of ‘cognitive maps’ to clarify the ways geographical knowledge may have been mentally coded.

Concerning the development and evolution of the latitude chart, work will proceed with the examination and comparison of the manuscript planispheres of the early modern period, extending the analysis from the Atlantic to the Indian and Pacific Oceans. An important goal of this study, which is being made in the scope of another doctoral research, is to better understand the linage of the nautical world charts of the period, starting with the Cantino planisphere (1502), and its reflex upon the printed maps and atlases of the sixteenth century. As for the broader questions concerning the nature, limitations and functions of the nautical chart in the early modern period, the research will proceed focusing on the intellectual discussions that took place among European scholars around the subject, and how cartographers dealt with the problem of magnetic declination.

Concerning the use of charts at sea, some progress is expected to be made through two independent actions: the examination of a sample of medieval and early modern charts with special lighting and multi-spectral analysis, searching fo
Latitude errors on Viladestes chart (1413), showing two distinct groups of cartographic data (BnF)
Facsimile of the Kunstmann III chart (c.1501-06) by Otto Progel, 1836 (BnF)
Print screen of Medea-Chart database showing an atlas of the 16th century
Carte Pisane (c.1290) with its implicit interpolated grid of meridians and parallels (BnF)