 However, the Antarctic continent was not discovered until the early 19th century.There are many maps from the 15th to the 18th century showing "Terra Australis Incognita" ("unknown land in the south"), the continent that should have been there, according to the Greek philosophers from Pythagoras onwards.They had worked out that the Earth was spherical, and had even calculated its diameter within a good degree of precision (Eratosthenes, in the 3rd century BCE), and thought that, as there were lands in the northern hemisphere, there should be lands in the southern hemisphere too, lest the world be unbalanced.