Accurate maps help keep ships safe at sea. In the thirteenth, fourteenth and fifteenth centuries, maps called "portolan charts" recorded the accumulated experience and wisdom of generations of Mediterranean seafarers. Portolan charts were practical, no-nonsense tools made for the use of sailors who sailed "great waters." As Tony Campbell, Map Librarian of the British Map Library put it so well: "The medieval mappaemundi (world maps in the Christian tradition) are the cosmographies of thinking landsmen. By contrast, the portolan charts preserve the Mediterranean sailors firsthand experience of their own sea, as well as their expanding knowledge of the Atlantic Ocean" (Campbell 1987, 372).

Campbell’s "Portolan Charts from the Late Thirteenth Century to 1500," is one of the essays in The History of Cartography, volume one (Cartography in Prehistoric, Ancient, and Medieval Europe and the Mediterranean) edited by J.B. Harley and David Woodward. This is the most important recent scholarly examination of portolan charts and their history, and anyone studying the pre-1500 portolan charts should refer to it. Campbell’s work has been essential to this commentary. Campbell summarizes existing research on portolan charts and suggests further study for a better understanding of them. Fewer than 100 portolan charts made prior to 1500 have survived. Of these, the three fifteenth-century portolan charts in the James Ford Bell Library at the University of Minnesota are the subject of this commentary.