(Latin: ) was a hypothetical continent first posited in antiquity and which appeared on maps between the 15th and 18th centuries. Its existence was not based on any survey or direct observation, but rather on the idea that continental land in the Northern Hemisphere should be balanced by land in the Southern Hemisphere. This theory of balancing land has been documented as early as the 5th century on maps by Macrobius, who uses the term on his maps. Names Other names for the hypothetical continent have included Terra Australis Ignota, Terra Australis Incognit''' ("the unknown land of the south") or Terra Australis Nondum Cognita ("the southern land not yet known"). Other names were Brasiliae Australis ("the southern Brazil"), and Magellanica ("the land of Magellan"). Matthias Ringmann called it the Ora antarctica (antarctic land) in 1505, and Franciscus Monachus called it the Australis orę (Austral country). In Medieval times it was known as the Antipodes. Change of name During the eighteenth century, today's Australia was not conflated with Terra Australis, as it sometimes was in the twentieth century. Captain Cook and his contemporaries knew that the sixth continent (today's Australia), which they called New Holland, was entirely separate from the imagined (but still undiscovered) seventh continent (today's Antarctica). In the nineteenth century, the colonial authorities in Sydney re-allocated the name Australia to New Holland and its centuries-old Dutch name eventually disappeared. Meanwhile, having lost its name of Australia, the south polar continent was nameless for decades until Antarctica was coined in the 1890s. In the early 1800s, British explorer Matthew Flinders popularized the naming of Australia after Terra Australis, giving his rationale that there was "no probability" of finding any significant land mass anywhere more south than Australia. The continent that would come to be named Antarctica would be explored decades after Flinders' 1814 book on Australia, which he had titled A Voyage to Terra Australis, and after his naming switch had gained popularity. Origins Ptolemy (2nd century AD) believed that the Indian Ocean was enclosed on the south by land, and that the lands of the Northern Hemisphere should be balanced by land in the south. Marcus Tullius Cicero used the term cingulus australis ("southern zone") in referring to the Antipodes in Somnium Scipionis ("Dream of Scipio"). The land (terra in Latin) in this zone was the Terra Australis. Legends of Terra Australis Incognitaan "unknown land of the South"date back