The idea that Atlantis was an actual historical place, and not just a legend invented by Plato, didn’t surface until the late 19th century. In his 1882 book, “Atlantis, the Antediluvian World,” the writer Ignatius Donnelly argued the accomplishments of the ancient world (such as metallurgy, language and agriculture) must have been handed down by an earlier advanced civilization, as the ancients weren’t sophisticated enough to develop these advances on their own. Assuming the Atlantic Ocean was only a few hundred feet deep, Donnelly described a continent flooded by shifting ocean waters that sank in the exact location Plato said it did: in the Atlantic Ocean just outside the “Pillars of Hercules,” the two rocks that mark the entrance to the Straits of Gibraltar. Long after modern oceanography and a greater understanding of plate tectonics poked holes.