Portolan Chart of the Mediterranean Sea
Cartographer: Martines, Joan
Medium: Ink and pigments on vellum
This is a portolan chart of the Mediterranean from a bound atlas dating from around 1550. It is the work of Joan Martines, a chart maker from Messina. Invented by mariners, portolan charts take their name from the Italian ‘Portolano’, meaning a written description of Catalan and Italian ports along a coastline. The first portolan Charts date from the late 13th century and represent an important change in the use of maps and charts. Until this point, most maps had held a religious significance and purpose, such as the medieval mappa mundi which was based on theological beliefs. The portolan chart contrasts with this tradition as they are based on direct observation and first hand experience and have a practical purpose. Reflecting their use by sailors they note only coastal locations, omitting most of the internal detail of the land. Place names are written at right angels to the coast, the more important ports in red ink. The lines which cover this and all other portolan charts are lines of constant bearing known as rhumb lines. These radiate from compass roses and allow the sailor to plot a course from harbour to harbour using dividers and straight edge.