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. It is four degrees wide on every side of the Pole, that is to say eight degrees altogether. Except that right under the Pole there lies a bare Rock in the midst of the Sea. Its circumference is almost 33 French miles, and it is all of magnetic Stone (...) This is word for word everything that I copied out of this author [Jacobus Cnoyen] years ago.

References

1. Nigra
2. Inventio Fortunata
3. Mount Qaf
4. 33 (number)
5. Phantom island
6. North Pole
7. North magnetic pole
8. Purgatorio
9. Maja e Thatë
10. List of monastic houses in Ireland
11. Mercator 1569 world map
12. Lasiodiplodia
13. Reichenau Glossary
14. List of descriptive plant species epithets (I–Z)