Often, islands come to represent places of extremes: They serve as utopias, purgatories, or ultimate dream vacation destinations. When it comes to mythological islands, utopias are especially popular. The Greeks had their Fortunate Islands, or Islands of the Blessed, where the luckiest mortals whiled away their time drinking and sporting. The Irish had a similar concept with their Mag Mell, or Plain of Honey, described as an island paradise where deities frolicked and only the most daring mortals occasionally visited.

But mythology isn't the only engine creating islands that don't actually exist—some of these legendary land masses popped up on maps after miscalculations by early explorers who interpreted icebergs, fog banks, and mirages as real islands. Some of these cartographic “mistakes” may have been intentional—certain islands depicted on medieval maps might have been invented so they could be named after the patrons who funded the explorations. Even explorer Robert E. Peary wasn't immune: Some say he invented "Crocker Land," a supposedly massive island in the Arctic, to secure funding from San Francisco financier George Crocker. Crocker Land didn’t exist, although that didn’t prevent major American organizations (including the American Museum of Natural History) from sponsoring a four-year expedition to find it.

Much like the fictional Crocker Island, here are 10 more imaginary isles, all of which have a place in world history, literature, or mythology—despite not having a place on the map.

1. Isle of Demons

Supposedly located off the coast of Newfoundland, this landmass (sometimes depicted as two islands) appeared on 16th century and early 17th century maps, and was named for the mysterious cries and groans mariners reported hearing through the mist.

The island was given a somewhat more solid identity after 1542, when nobleman and adventurer Jean-François Roberval was instructed by the King of France to found settlements along the North Atlantic coast. He brought his niece, Marguerite de La Rocque de Roberval, along for the voyage, but she began a passionate affair with one of Roberval's officers. Annoyed, Roberval put his niece (and maybe the officer—accounts differ), as well as her nurse, ashore on an otherwise unspecified "Isle of Demons" in the St. Lawrence River. Marguerite gave birth on the island, but the child died, as did Marguerite’s lover and nurse. However, the plucky Marguerite survived alone for several years, using her firearms against the wild beasts. After being rescued by Basque fishermen and returning to France, she reported that she had been beset "by beasts or other shapes abominably and unutterably hideous, the brood of hell, howling in baffled fury."

Marguerite’s story appears in several historical accounts, including versions by Franciscan friar André Thevet and the Queen of Navarre. Still, the location of the “Isle of Demons” has never been found for certain. Maritime historian and veteran Atlantic sailor Donald Johnson thinks he has identified it as Fichot Island, close to the Strait of Belle Isle at the northern tip of Newfoundland. Johnson notes that Fichot Island lies on Roberval's course, and is home to a breeding colony of gannets—a type of seabird whose guttural cries, heard only while breeding, may have been taken for the sounds of demons.

2. Antillia

Also known as the Isle of Seven Cities, Antillia was a 15th century cartographic phenomenon said to lie far west of Spain and Portugal. Stories about its existence are connected to an Iberian legend in which seven Visigothic bishops and their parishioners fled Muslim conquerors in the eighth century, sailing west and eventually discovering an island where they founded seven settlements. The bishops burned their ships, so they could never return to their former homeland.

According to some versions of the legend, many people have visited Antillia but no one has ever left; in other versions of the tale, sailors can see the island from a distance, but the land always vanishes once they approach. Spain and Portugal even once squabbled over the island, despite its non-existence, perhaps because its beaches were said to be strewn with precious metals. By the late 15th century, once the North Atlantic was better mapped, references to Antillia disappeared—although it did lend its name to the Spanish Antilles.

3. Atlantis

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First mentioned by Plato, Atlantis was supposedly a large island that lay "to the west of the Pillars of Hercules" in the Atlantic Ocean. It was said to be a peaceful but powerful kingdom lost beneath the waves after a violent earthquake was released by the gods as punishment for waging war against Athens. There have been many attempts at identifying the island, although it may have been entirely a creation of Plato’s imagination; some archeologists associate it with the Minoan island of Santorini, north of Crete, whose center collapsed after a volcanic eruption and earthquake around 1500 BCE.

4. Aeaea

In Greek mythology, Aeaea is the floating home of Circe, the goddess of magic. Circe is said to have spent her time on the island, gifted to her by her father, the Sun, waiting for mortal sailors to land so she could seduce them. (Afterwards, the story goes, she would turn them into pigs.) Some classical scholars have identified Aeaea as the Cape Circeium peninsula on the western coast of Italy, which may have been an island in the days of Homer, or may have looked like one because of the marshes surrounding its base.

5. Hy-Brasil

Also known as Country o'Breasal, Brazil Rock, Hy na-Beatha (Isle of Life), Tir fo-Thuin (Land Under the Wave), and by many other names, Brasil (Gaelic for "Isle of the Blessed") is one of the many mythical islands of Irish folklore, but one that nevertheless made several appearances on real maps.

Like the Mediterranean's Atlantis, Brasil was said to be a place of perfect contentment and immortality. It was also the domain of Breasal, the High King of the World, who held court there every seven years. Breasal had the ability to make the island rise or sink as he pleased, and normally only let the island be visible when his court was in full swing.

According to legend, Brasil lay "where the sun touched the horizon, or immediately on its other side—usually close enough to see but too far to visit." It first appeared on a map made in 1325 by Genoese cartographer Daloroto, who depicted it as a large area to the southwest of Ireland. (Later maps placed it farther west.) Its shape was usually drawn as a near-perfect circle, bifurcated by a river. Numerous explorers searched for the island, and some, including Italian navigator John Cabot (Giovanni Caboto), even claimed to have found it.

Today, scholars think Brasil may have been a reference to Baffin Island, or to now-sunken lands visible only when sea levels were lower during the last Ice Age, or else an optical illusion produced by layers of hot and cold air refracting light rays.

6. Baralku

Among the indigenous Australians of the Yolngu culture, Baralku (or Bralgu) is the island of the dead. The island holds a central place in the Yolngu cosmology—it's where the creator-spirit Barnumbirr is said to live before rising into the sky as the planet Venus each morning. Baralku is also the spot where the three siblings who created the landscape of Australia, the Djanggawul, originated. The island supposedly lies to the east of Arnhem Land in Northern Australia, and the Yolngu believe their souls return there after death.

7. Saint Brendan's Isle

This piece of land was said to have been discovered by Irish abbot and traveler Saint Brendan and his followers in 512, and to be located in the North Atlantic, somewhere west of Northern Africa. Brendan became famous after the publication of the Latin Navigation of St Brendan, an 8th/9th century text that described his voyage in search of the wonderful "Land of Promise" in the Atlantic Ocean. The book was a medieval best-seller, and gave the saint his nickname, "Brendan the Navigator." The island was said to be thickly wooded, filled with rich fruit and flowers. Tales of St. Brendan's Isle inspired Christopher Columbus, among others, and had an important influence on medieval cartography. Sightings were reported as late as the 18th century.

8. Avalon

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First mentioned in Geoffrey of Monmouth’s 12th century Historia regum Britanniae, Avalon is the place where the legendary King Arthur's sword is said to have been forged, and where he was sent to recover after being wounded in battle. The island was said to be the domain of Arthur's half-sister, sorceress Morgan le Fay, as well as her eight sisters. Starting in the 12th century, Avalon was identified with Glastonbury in Somerset, in connection with Celtic legends about a paradisiacal “island of glass.” Twelfth century monks at Glastonbury Abbey claimed to have discovered Arthur’s bones—although later historians believe their “discovery” was a publicity stunt to raise money for Abbey repairs.

9. Island of Flame

In ancient Egyptian mythology, the Island of Flame (also known as the Island of Peace) was the magical birthplace of the gods and part of the kingdom of Osiris. It was said to have emerged out of primeval waters and to lay far to the East, beyond the boundaries of the world of the living. Associated with the rising sun, it was a place of everlasting light.

10. Thule

For the Greeks and Romans, Thule existed at the northernmost limit of their known world. It first appears in a lost work by the Greek explorer Pytheas, who supposedly found it in the 4th century BCE. The Greek historian Polybius says that "Pytheas ... has led many people into error by saying that he traversed the whole of Britain on foot … and telling us also about Thule, those regions in which there was no longer any proper land nor sea nor air, but a sort of mixture of all three of the consistency of a jelly-fish in which one can neither walk nor sail, holding everything together, so to speak." Later scholars have interpreted Thule as the Orkneys, Shetlands, Iceland, or possibly Norway, while the Nazis believed Thule was the ancient homeland of the Aryan race.

Bonus: California

Between the 16th and the 18th centuries, many Europeans believed that California was an island. Like other islands on this list, the place was reported as being a kind of paradise. In fact, the name "California" first appears in a romantic novel penned by Spanish author Garci Ordóñez de Montalvo, who described it as an island filled with gold and precious gems, populated by a race of Amazons who rode griffins.

This list was republished in 2019.