Lemuria is the sister-city of Atlantis in ancient times.
Like Atlantis, Lemuria sank beneath the oceans. After countless centuries its inhabitants, the Lemurians evolved into serpent-like beings, and no longer resembling to their Atlantean cousins. Lemuria remained lost to Atlantis until contact was reestablish in open hostilities.
By the modern day, Lemuria resurfaced as a hostile nation towards Atlantis.