Open any nineteenth century navigational chart of the Atlantic Ocean and what is immediately apparent is the proliferation of rocks, shoals, islands and other hazards that litter almost every corner of the ocean. Known to seamen as 'vigias', these were dangers whose existence rested on authentic, documented sightings. Yet amazingly none of these supposed hazards had any real existence. What is the story behind these mysterious vigias? Raymond Howgego offers a unique study of this intriguing phenomenon. He identifies more than three hundred such vigias, providing exact locations, details of their original discovery and those who discovered them, as well as Admiralty expeditions despatched to investigate them. Based upon extensive personal research of every known Atlantic chart, original logs, nautical journals and directories, together with multilingual sources, and with an annotated critical bibliography, the result is a compelling account of an intriguing phenomenon of geographical discovery, maritime history and nautical culture.