mountain goes back at least to Roman times, but the author of Inventio Fortunata added other features to the picture as well as measurements. Whether or not the Inventio is the source of the medieval concept of the North Pole as a magnetic mountain surrounded by a circular continent divided by four powerful rivers, maps as early as Martin Behaim's 1492 globe depict the region in this way. Johannes Ruysch's Universalior cogniti orbis tabula from 1508, features a marginal note mentioning the Inventio Fortunata: "It is said in the book concerning the fortunate discovery [Inventio Fortunate] that at the arctic pole there is a high magnetic rock, thirty-three German miles in circumference. A surging sea surrounds this rock, as if the water were discharged downward from a vase through an opening. Around it are islands, two of which are inhabited." Gerardus Mercator's world map of 1569 reflects his reading of Cnoyen's Itinerarium. It also features a marginal note alluding to the Franciscan's "discovery", but not to the book itself, which he never saw: "we have taken [the Arctic geography] from the Itinerium of Jacobus Cnoyen of the Hague, who makes some citations from the Gesta of Arthur of Britain; however, the greater and most important part he learned from a certain priest at the court of the king of Norway in 1364. He was descended in the fifth generation from those whom Arthur had sent to inhabit these lands, and he related that in the year 1360 a certain Minorite, an Englishman from Oxford, a mathematician, went to those islands; and leaving them, advanced still farther by magic arts and mapped out all and measured them by an astrolabe in practically the subjoined figure, as we have learned from Jacobus. The four canals there pictured he said flow with such current to the inner whirlpool, that if vessels once enter they cannot be driven back by wind." The Arctic map inset on Mercator's 1569 world map was the prototype for the influential and widely circulated Septentrionalium Terrarum of 1595, posthumously published by his son, and the maps in Ortelius's Theatrum Orbis Terrarum of 1570. Both show the same configuration of the arctic regions as the 1569 map. In his letter to Dee, Mercator further quotes Cnoyen's description of the Northern regions: "...In the midst of the four countries is a Whirlpool into which there empty these four Indrawing Seas which