North Atlantic Ocean
Namor the Sub-Mariner (King)
Points of Interest
City of Atlantis (Capital), the Hydrobase, City of Kamuu, Cave of Shadows, Namor's solitary place, Realm of the faceless ones, Tomb of Princess Fen, ruins of Tha-Korr
Atlantis is completely under water, therefore it has many features that differ from the surface continents. Atlantis is also the only location of the Homo mermanus species.
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Atlantis was a moderately sized continent roughly the size of modern Australia with many human settlements, before an event occurring 21,000 years ago called the "Great Cataclysm" caused it to submerge into the sea. The inhabitants had built an enormous glass-like dome over the captial city, also known as Atlantis, and when barbarians sent by the Deviant Lemuria empire attacked Atlantis, King Kamuu opened the magma-pits, the city's means of heating, causing a chain reaction which collapsed and sank the continent.
A few settlements survived the catastophe, such as the city of Netheria. Priests and intellectuals foresaw the Lemurian attack and fortified their city, thus keeping it intact as the continent sank. Netheria exists to this day, ruled by Queen Kala.
About 8,000 years ago, a group of Homo mermani nomads discovered the ruins of the capitol city of Atlantis, making it and other ruined human settlements their home. Eventually, they salvaged as much of the sunken wreckage as possible and established their own society. Thus, these people were thereafter referred to as Atlanteans, as it is in the city of Atlantis that their first complex society emerged.
500 years after the settlement of the new undersea Atlantis, another group of Homo mermani ventured out to establish their own city--this time in the undersea ruins of Lemuria, another continent submerged during the Great Cataclysm. These "Lemurians", as they then called themselves, discovered an artifact known as the Serpent Crown in the ruins of their adopted city. Crafted by ancient Atlantean alchemists, the Serpent Crown was a vessel empowered by the demonic Elder God Set. With exposure to and extensive use of the ancient mystical device by their leader, Naga, the Lemurians would eventually become more serpent-like in appearance than their Atlantean cousins.
The Atlanteans had little to no contact with their human cousins for millenia, until the 20th century when the two races would come into sustained, often hostile, contact, when the Atlanteans would make military strikes on surface populations. The Atlantean Prince Namor, the Sub-Mariner, was initially hostile to the surface world, and has occasionally drifted back to his anti-human perspective, but has eventually grown to ally himself with the surface, most notably during the Second World War when Namor led the forces of Atlantis alongside the Allies against the Axis of Evil. Namor remains the reigning Prince of Atlantis to this day.