Marvel's version of Atlantis first appeared in Motion Picture Funnies Weekly #1, in April 1939 , but it wasn't named Atlantis until the October 1963 issue of Fantastic Four Annual #1. In the Marvel universe, Atlantis is a the city under the sea ruled by Namor, the Sub-Mariner.
It was originally a small continent with human settlements but this all changed 21,000 years ago during an event known as the Great Cataclysm and it was swallowed by the depths of the sea. This event was caused by King Kamuu when he tried to defend it from the Deviants of Lemuria by opening the city's magma pits. Several settlements survived including Atlantis and Netheria, as they had built a glass dome to shield each before this catastrophe took place.
Sole survivors included such beings as Varnae, Stygyro and Dakhimh the Enchanter. But it was only 13,000 years later than the city of Atlantis was re inhabited, as it was discovered by some Homo Merman's who made it their first mighty city, and becoming the Atlanteans.
After 500 years living in Atlantis another city was rebuilt, Lemuria, by Atlanteans who left Atlantis. And so it was that the Lemurians differed from their former people when they discovered the Serpent Crown in their ruins and they began to develop a more serpentine appearance.
Homo Sapiens and Homo Mermanus have interacted several times, usually with hostility as the Homo Mermanus have invaded the surface world multiple times. Though the current ruler of Atlantis, Prince Namor fought against the Axis Powers in World War II.
In modern times, the Old Kingdom of Atlantis revealed itself and claimed rule to all of the sea. Namor went to war with them, but the war was stopped as soon as it began when the Invisible Woman became its ruler.
DC's version of Atlantis first appeared in Adventure Comics vol 1 #260 in 1959. In the DC universe, Atlantis is the city under the sea ruled by Aquaman.
The Kingdom of Atlantis is generally considered to be the earliest known civilization on Earth, existing as long as 1,000,000 years ago. How the Atlantean race of homo sapiens arose hundreds of thousands of years before the rise of current-day humanity is unknown, but this anomaly of evolution is believed to be linked to the strong presence of magical energy, or mana, that then existed around Earth.
The original Atlanteans were highly mystical beings; their society and the very structure of the world was based on the use of this magical energy. Over the millennia, the mana was eventually depleted, and the powers of science and technology replaced sorcery as the dominant force of nature.
While it flourished, Atlantis was a great civilization; it ruled the world through the power of its twelve major city-states, which were located on all the continents of Earth. Each of these city-states was ruled by a sorcerer-monarch who wielded the mystic power of his part of the world. At the head of the entire Atlantean Empire was the most powerful kings and queens. Less the master of the eleven other monarchs than a sort of chairman of the Royal Conclave of Twelve, this monarch also reigned over the first and largest of the Atlantean city-states, the magnificent City of the Golden Gate.
In its early years however, Atlantis was ruled by a body of mad sorcerers. These sorcerers were eventually wiped out and replaced by saner rulers who sought peace rather than the the endless warfare of their predecessors. Atlantis' first great era of peace and prosperity came during the reign of Calculha, about half a million years ago. To Calculha and his queen Majiestra were born two sons, Ahri'ahn and Garn. Majiestra was a student of the dark forces, and in seeking power, she stole the Twelve Crystals of the Zodiac, which were keyed to the magical nexi of the twelve major cities. To save Atlantis from her evil Ahri'ahn sacrificed himself. His soul was sent out into the stars in the form of pure magical energy, where it traveled for hundreds of thousands of years before being drawn back to Earth for its rebirth as Arion.
The Atlanteans grew in stature and power. Soon, their eyes turned to the world beyond Earth, leading them to begin an extensive study and survey of the universe. These efforts culminated in the creation of magically-fueled spacecraft, which carried hordes of Atlantean colonists out into interstellar space, they lost contact with Earth. Years later, it was learned that the farther they traveled away from Earth, the weaker the magic that propelled their ships became. The Atlanteans found refuge on an uninhabited world and created a civilization based on science. Technology-powered space flight was eventually rediscovered and the Atlanteans, having evolved along different biological and ethical paths, set out on a warlike conquest of neighboring worlds.
Although the Atlanteans were virtually the all-powerful masters of the world and their environment, they were confronted with certain insurmountable problems. Foremost among these problems was the disappearance of the magical mana. Also, the Atlanteans encountered a savage race of barbaric sub-men, Homo Erectus, which were the precursors to our own civilization. The people of Atlantis also shared the Earth with a variety of magical beings and creatures, as well as otherdimensional visitors from neighboring mystically-based realms.
As the magic waned, Atlantis' hold over the Earth began to weaken as all of the Atlanteans' energies were focused on maintaining their hold on existence. Cities built on magic crumbled, and the creatures of sorcerous origins lapsed into extinction and myth. Arion had returned during this era and attempted to gold his world together, but the forces of change were to great for even his magic, and the great civilization that was Atlantis crumbled.
The kingdom of Atlantis held on for several years after that, with Arion at it's helm, before the final fall and the Atlanteans' virtual extinction at the hands of the barbarous hordes of emerging mankind. Before this, Lord Norrad the Younger fled Atlantis with a small group of followers. They eventually sailed through the interdimensional nexus linking the Earth and Skartaris.
Cities of Atlantis
Atlantis has split into several different cities since its sinking. The main of these being Poseidonis, the domed city where Aquaman is seen most often, but there are many more.
The main city of Atlantis, it is a large domed city. Aquaman is seen here most often. It is the location of the King's throne. It was destroyed by the Spectre, during Infinite Crisis, on his rampage against magic. Garth tried to stop it but was unable to. It has been rebuilt now.
A land of rough living mermen and women that view their way of life (living with the creatures of the deep) clean and natural, feeling it makes them stronger. This was the home of the Merman King Iqula, whom challenged and nearly defeated Aquaman. After being defeated in a one-on-one battle with Aquaman he swore to help protect Poseidonis as best he can.
Thierna Na Oge
A land of mystics that are ruled by a mystical Conclave.
Shayeris (formerly Crastnus)
The Capital of the Hidden Valley. Home to extremely secluded mystics and pacifists. The birthplace of Garth the first Aqualad.
Xebel is a penal colony locked beneath the Bermuda Triangle, Mera is from here. Mera's father rules in Xebel. Recently Mera's sister Siren has been sent from Xebel to kill Aquaman along with some Xebel soldiers. It's unclear how she and the soldiers managed to get out of their imprisonment.
Sub Diego was a portion of San Diego that sunk into the sea, and became part of the kingdom of Atlantis. Some of the people who sunk with the part of the city gained the ability to breath water. One of these people was Lorena Marquez who became Aquagirl when granted her powers.
In Plato's Timaeus, he gives a brief account of Atlantis. The day after the Republic, one of Socrates' friends, Critias, recounts a marvelous tale of the ancient civilization. Apparently, Atlantis had been one of the dominant societies of the past, threatening to over-take almost all of the civilizations around the Mediterranean Sea. It wasn't until Athens stood against Atlantis that it had faced any threats. One night, the entire Atlantean army sank into the ground. And, the island of Atlantis (which had been located on the Straight of Gibralter) plummeted beneath the sea.
The tale is expounded on in Plato's other work, Critias.