right|thumb|250px|The oldest original cartographic artifact in the nautical chart of the
Mediterranean Sea. Second quarter of the fourteenth century./" class="wiki">Library of Congress: a portolan
nautical chart of the
Mediterranean Sea. Second quarter of the fourteenth century.
Portolan charts are navigational maps based on realistic descriptions of harbors and coasts. They were first made in the 1300s in
Italy,
Portugal and
Spain. With the advent of the
Age of Discovery, they were considered State secrets in Portugal and Spain, very valuable in the description of
Atlantic and
Indian coastlines for newcomer
English and
Dutch raiding ships. The word
portolan comes from the
Italian adjective
portolano, meaning "related to ports or harbours."
Contents & themes
These charts, actually rough maps, were based on accounts of medieval Europeans who sailed the
Mediterranean and
Black Sea coasts, and later were used to map coastal resources in the
Atlantic and
Indian oceans. At the beginning of the
Age of Discovery they would describe the coast of
Africa,
Brazil,
India and even past the
Strait of Malacca into
Japan, knowledge vital for the slow rise to prominence of the English Armada and of Dutch merchants, that followed in the
Iberian Powers wake. Frequently drawn on sheepskin, portolan charts show coastal features and ports. In earlier days, what could be used as a harbor encompassed more of the coastline than now, as ships were smaller, they might need to seek refuge in a harbor more often, and some ships were
intentionally beached for maintenance and repairs. Thus, nearly any protected bay or flat beach might be of interest to mariners, not only for safe harbor but also as previous coastal
reconnaissance.
The straight lines criss-crossing many portolan charts represent the thirty-two directions (or headings) of the mariner's compass from a given point. This is similar to the
compass rose displayed on later maps and charts. Naming or demonstrating all thirty-two points is called
boxing the compass.
The portolan combined the exact notations of the text of the
periplus or pilot book with the decorative illustrations of the conceptual
T and O map. In addition, the charts offered a realistic depiction of the shore, and they were meant for practical use by a mariner of the period.
Portolans failed to take into account the curvature of the earth; as a result, they were unhelpful in crossing the open ocean, as navigational tools. Instead they derived their use in close quarters identification of landmarks.
Portolani were useful for navigation in smaller bodies of water, such as the
Mediterranean,
Black, or
Red Seas.
The oldest extant version
The oldest extant portolan is the
Carte Pisane, dating from approximately 1296. The cartographer
Angelino Dulcert produced a portolan in 1339.
See also
