The charts known as portolani, or portolans, as the name suggests, were developed to show mariners how to reach and safely navigate the ports of the medieval world’s maritime entrepôts, great and small. Let’s learn more.
The Crucial Role of Compass
Initially, the charts were drawn up for the densely traveled waters of the Mediterranean or the Bay of Biscay—the northeastern Atlantic seaboard stretching from the northwestern tip of Iberia, Cape Finisterre, to the British Isles. Their making, beginning around the middle of 13th century, was facilitated by the arrival of the compass, which had been brought to Afro-Eurasia from China.
In both detail and utility, portolan charts were very different from contemporary mappae mundi, that is “world maps” based on ancient Tau Omega or zonal maps, which imagined the three known continents as surrounded by a spherical ocean. Nor were portolan charts usually ringed by dragons or the “monstrous races” imagined to lurk beyond the frontiers of maritime exploration. They were starkly pragmatic and oriented to the cardinal points of the compass, rather than to Jerusalem as the center of the world.
Oldest Portolan Chart
The oldest portolan chart that survives—ragged from use and exposure to seawater and weather—is the so-called Carta Pisana, the Pisan Map, although it was probably made in Genoa.
Its material support—the hide of a calf whose neck is still clearly visible—was inscribed with a scale and a series of rhumb lines intersecting two systems of tangent circles measuring 38 or 39 centimeters apiece; the entire artifact measures 43 by 103 cm or about 17 by 40 inches—a bit more than an arm’s length.
On this chart, the names of prevailing winds are prominently framed in red and situated in their proper quadrants: tramontana, greco, levante, silocco, mexjorno, ponente, mentro. Coasts are outlined in black, with the mouths of rivers left blank. Reefs are indicated by groups of red crosses around islands and near some coasts. Clearly visible are the Mediterranean, the western part of the Black Sea, and the eastern Atlantic coastline from Azenmour, in North Africa, as far as the Rhine, north of the then-great port of Bruges.
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Not Exactly Accurate
However, the mapmakers’ knowledge of the Atlantic seaboard, or interest in it, is clearly minimal. In contrast to the central focus of the map, which is realistic and highly detailed, the blob standing in for England, Isla Engleterra, is a mere placeholder.
The only place of real interest here is the coast of Kent, as that was the site of the civitate dobra sancto Thomás de Cónturba—the great pilgrimage shrine of Saint Thomas Becket at Canterbury, second only to Jerusalem and Santiago de Compostela as an attraction to travelers. By contrast, the Thames and civitate Londra are randomly placed on the chart, Cornoalla is hastily sketched, and the great southern port of Southampton is mislabeled as Stanfort.
There is also little interest, here, in the European interior, which is weirdly distorted. And while major maritime ports are named, the only other place of relevance appears to be Isula Bilela—the island of Belle-Île-en-Mer, off the Breton coast.
Yet, the fact that this chart’s place-names are rendered in a mixture of dialects—a maritime lingua franca or contact vernacular—is a fascinating indicator of how it must have been made, and by whom, since the specialized knowledge of the person or persons who wielded compass, caliper, and pen was clearly supplemented by the expert and lived knowledge of mariners—notably the Genoese, who knew the Mediterranean intimately and especially the Tyrrhenian Sea, dominated by Genoa at this date.
A More Recent Chart
This older chart’s degree of detail and potential uses is nicely contrasted by a chart created in Portugal by Jorge de Aguiar in the auspicious year of 1492. It thereby shows us a state-of-the-art snapshot of this same region on the eve of the voyage that could not have been undertaken without such charts—and that would soon complicate and expand the medieval world they depicted.
Also made of parchment, but of a superior quality and state of preservation, this later chart shows how much knowledge had been accumulated by mariners in the course of the two centuries that had elapsed between the two.
The entire Mediterranean littoral and Black Sea coast are rendered in exquisite detail, and trans-Alpine Europe, with some major rivers, takes on more realistic contours. The eastern Atlantic coast and British Isles receive more substantial treatment and, most importantly, the entire coast of West Africa and outlying islands—already being explored and colonized by the Portuguese—are represented accordingly.
Why Were Portolan Charts Important?
Portolan charts, then, are the indispensable medieval instruments that reflected the interconnectivity of the medieval world and enabled the networks of trade, travel, and communication that were linking the ports of the eastern Atlantic to those of the Mediterranean and Black Sea, as well as to the maritime and overland roads to Asia and Africa.
They distilled, but also expanded, accumulated knowledge of those linkages, and emboldened the mariners who pushed past their porous boundaries in subsequent centuries.
Common Questions about Navigating the Medieval Seawaters with Portolan Charts
The oldest portolan chart that survives is the so-called Carta Pisana, the Pisan Map.
Portolan charts are the indispensable medieval instruments that reflected the interconnectivity of the medieval world and enabled the networks of trade, travel, and communication that were linking the ports of the eastern Atlantic to those of the Mediterranean and Black Sea, as well as to the maritime and overland roads to Asia and Africa.
The portolan charts were starkly pragmatic and oriented to the cardinal points of the compass, rather than to Jerusalem as the center of the world.