Coastal navigation required charts, though most coasting vessels stayed within sight of land. Submerged rocks and shipwrecks, sandbars, treacherous currents, and estuaries were indicated in the better portolan charts, whose cartographic accuracy was impeccable. To aid sailors as they navigated, por-tolan charts also featured iconic depictions of port cities and prominent topographic elements, such as mountains and lighthouses. Several extant portolan charts have small holes around the edges, suggesting that these charts were either nailed to a table or wall or laced with cord and mounted on a frame. Pinpricks in the center of wind roses indicate that a measuring compass was centered in the middle of the winds and rotated in an arc to determine sailing directions. During the early Renaissance, ships from Genoa, Venice, Marseilles and Catalan ports dominated the Mediterranean, sailing mostly along the coasts with the aid of portolan charts, a magnetic compass, and an astrolabe, an instrument used by Islamic astronomers. During the 16th century, the most famous northern port for navigators was Dieppe, on the coast of France, whose cartographic school was renowned for its portolan charts. Besides coasting south to the mouth of the Mediterranean, sailors from Dieppe ventured to Africa and across the Atlantic. By the late 15th century, sailors realized that the magnetic compass did not take into account the magnetic declination of the Earth, and the azimuth compass was invented. This instrument contributed to the accuracy of navigation in general. With the astrolabe (“star taker”), sailors could fix their position within a specific latitude.
World History
