The treaty that drew the first borders of the newly established United States after the Revolutionary War refers to an island that does not exist. The northern boundary of the new nation, the 1783 Treaty of Paris declared, shall pass “through Lake Superior northward of the Isles Royal and Phelipeaux.” It sounds clear enough, but when surveyors went out to map the border in the 1820s they discovered a problem: Isle Phelipeaux was not there.

The long and fascinating history of such phantom islands is the topic of Malachy Tallack’s new book, The Un-Discovered Islands, which he discussed recently in an interview with National Geographic. Inspired by the book, we’ve rounded up a collection of vintage maps that feature islands that don’t actually exist.

“Frisland,” for example, appears to have been the invention of a wealthy Venetian named Niccolò Zeno, who wrote a book in 1558 claiming that his ancestor had discovered the New World before Columbus. Historians now consider the claim bogus, but it was influential at the time, and the islands it described appeared on maps for more than a century. This was, after all, the era when people were just beginning to explore the world’s oceans, and news traveled slowly by modern standards.

Some islands were believed to have existed and later sunk. Sarah Ann Island, a speck of land in the Pacific Ocean claimed by the United States under the 1856 Guano Act, a law permitting the appropriation of islands covered with bird droppings (a valuable source of fertilizer at the time). The island happened to be in the path of a total solar eclipse in 1937, but when astronomers went to seek it out, the island was gone. Most likely it had never been there, but newspapers reported that it had sunk, and the rumor stuck.

Other “un-discovered” islands, like Phelipeaux, appear to be the result of outright fraud. This island appears on a map by a Virginia-born British loyalist named John Mitchell that was used by both sides to negotiate the Treaty of Paris (see below). Mitchell isn’t at fault for the faux island, however. He simply copied the island from an older map.

The island’s name, together with the names of three other nonexistent Lake Superior islands, Pontchartrain, Maurepas, and St. Anne, betray the origin of the ruse. In the 1720s, a count named Jean-Frédéric Phélypeaux had served as a French secretary of state. He happened to have estates named Pontchartrain and Maurepas, and his family’s patron saint just happened to be St. Anne. Apparently, someone was kissing up to the count by inventing islands named in his honor.

The sycophant appears to have been an explorer named Pierre François Xavier de Charlevoix, whose voyages in the region had been funded by the good count Phélypeaux. The four imaginary islands first appear on a map commissioned for a book published by Charlevoix in 1744. The fraud went undetected for nearly a century until another treaty finally erased them from maps for good in 1842.

“This little lie that an explorer told became entangled in a really important part of history,” Tallack says. “I find that really fascinating.”

One of the most recent island un-discoveries happened in 2012, when an Australian research vessel reported that Sandy Island, which maps depicted off the coast of New Caledonia in the South Pacific, was most definitely not there. Within weeks the National Geographic Society announced that Sandy Island would be stricken from all of its maps, and other mapmakers followed suit.

Google removed Sandy Island from its maps, too, but people continued to post photos at its former location. The photos were mostly meant as a joke, Tallack says, but they also hint at the powerful pull islands exert on the human imagination. “Because their borders are well defined we can project our ideas onto them much more easily than we can with other places.”

If you’re interested in maps of maritime curiosities, you might enjoy our previous posts about 19th century ships buried under the streets of San Francisco or the quest for the Northwest Passage.