 The "Atlantis" part of the legendarium explores the theme of the memory of a 'straight road' into the West, which now only exists in memory or myth, because the physical world has been changed.The "Akallabêth" says that the Númenóreans who survived the catastrophe sailed as far west as they could in search of their ancient home, but their travels only brought them around the world back to their starting points.Hence, before the end of the Second Age, the transition from "flat Earth" to "round Earth" had been completed.