Rupes Nigra

The Rupes Nigra ("Black Rock"), a phantom island, was believed to be a black rock located at the Magnetic North Pole or at the geographic North Pole itself.

Described by Gerardus Mercator as 33 French miles in size, it provided a supposed explanation for why all compasses point to this location.

The idea came from a lost work titled Inventio Fortunata, and the island featured on maps from the sixteenth and seventeenth centuries, including those of Mercator and his successors.

Mercator described the island in a 1577 letter to John Dee: In the midst of the four countries is a Whirl-pool, into which there empty these four indrawing Seas which divide the North.

And the water rushes round and descends into the Earth just as if one were pouring it through a filter funnel.