Great Subterranean Empires
A catch-all term in the fields of archaeology and history for empires said to have disappeared beneath the Earth and the waves between 10,000 and 15,000 years ago.
Some of these empires seem to have significant history on Earth, while others seem to spring up overnight at some point in the historical record. The question of whether the Prehistoric Martian Super-Civilization and Protoculture were related to or aware of the Great Subterranean Empires remains under debate.
Known Great Subterranean Empires include:
Scholarship regarding pre-Xia dynasty China remains spotty on this topic; while pre-Xia emperors had been claimed as existing roughly 5,000 years ago, at least one strain of scholarship suggests they came from a Great Subterranean Empire on the Asian mainland.