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

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Charting the origin, evolution and use of nautical cartography

MEDEA-CHART has helped unravel the medieval origin of nautical charts, explaining their critical role in maritime expansion, as navigational instruments and representations of newly discovered lands.

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Medieval and early modern nautical charts served three main interconnected functions: as repositories of information, especially navigational; as voyage planning tools; and to determine the position of ships at sea. As such, they were essential to European oceanic voyages and a key resource during the maritime expansion. Although charts have been studied for at least 200 years, critical questions related to their genesis, methods of construction and use at sea have proved largely intractable. “This was due to the complexity of the subject, which demands a deep knowledge of the navigational and charting methods of the time, a requirement not normally within reach of traditional historians of cartography,” explains Joaquim Alves Gaspar, coordinator of the MEDEA-CHART project, which was funded by the European Research Council. That is why MEDEA-CHART adopted a multidisciplinary research approach, involving scholars from diverse backgrounds, including the history of science, history of art, marine navigation and mathematical cartography. The project’s findings shed light not only on when, and how, the first charts were constructed, but also their influence on geopolitics.

Charting a route through complexity

The team studied nautical charts from the 13th to the 17th centuries kept in various archives around the world. To date manuscripts, reveal graphical content and detect marks of drafting and use, a range of techniques including radiocarbon dating, hyperspectral analysis and microscopy were applied on-site. The project developed a database to store information and high-resolution reproductions, which were examined with cartometric methods, in order to characterise their geometry and better understand how they were constructed. This analysis was complemented by computer simulations, which aimed to reproduce those same geometric features by numerically simulating the construction methods described in textual sources.

Key discoveries

MEDEA-CHART’s approach helped clarify some fundamental historical issues, in particular those related to the genesis, purpose and construction methods of the earliest charts. “With our contribution, the medieval origin of the portolan chart is now largely accepted and a meaningful connection between charts and navigation has been established,” notes Gaspar. The project also brought attention to a heated debate between cosmographers, pilots and chart makers, after the Magellan and Elcano circumnavigation (1519-1522), over chart distortions caused by magnetic declination, a physical phenomenon which affected the accuracy of the marine compasses. The discussion was triggered by the realisation that the coveted Moluccas Islands – placed within the Spanish hemisphere according to contemporaneous Portuguese charts – were in fact within the Portuguese hemisphere, according to the terms of the Treaty of Tordesillas. “So, the longitudinal distortions caused by magnetic declination went from a technical detail, irrelevant to marine navigation, to a pivotal political issue among competing imperial states,” adds Gaspar.

A lasting legacy

While COVID-19 curtailed some of the on-site international study of manuscript charts, it galvanised the development of the project’s database, currently containing information and images on thousands of charts and atlases. Equipped with powerful search and visualisation tools, it is now freely available for researchers. In May 2023, the project’s final exhibition, ‘What is a Nautical Chart, really?’, was launched at the Hydrographic Institute, Lisbon. It will later tour different cities of Portugal, aiming to reach a wider audience. One of the final outcomes of the project was the publication of the book ‘The Cartography of Magellan’. “Written for a non-specialist readership, the book resolves several historical questions, arguing for example, that an important but enigmatic Portuguese chart kept in Istanbul was used as evidence in the contentious 1524 negotiations between the Spanish and Portuguese Crowns,” says Gaspar.


MEDEA-CHART, medieval, navigation, nautical chart, cartography, radiocarbon dating, portolan chart, manuscript, Portugal

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