Attilan is the ancestral home of the Inhumans, a highly advanced offshoot of the human race. About seven thousand years ago, the Inhumans grew tired of centuries of persecution by their more primitive parent race, and decided to create a place of refuge for themselves. Under the leadership of King Myran, the Inhumans chose as a site for their city a small island in the northern Atlantic Ocean, located about two hundred miles southwest of Iceland. The city, which took several decades to complete, was named Attilan, a name derived from Atlantis, the former pinnacle of civilization on Earth that had vanished beneath the sea about three millennia before. Attilan has been the sole center of the Inhuman population ever since.
For millennia, the Inhumans dwelt in Attilan, isolated from contact with mainstream humanity except for an occasional encounter with a lost Greek or Viking sailing vessel. Finally, in the mid-Twentieth Century, with the advent of steamships and airplanes, the Inhumans began to fear discovery by the human race. When one of his subjects was captured by human beings, young king Black Bolt determined that the Inhumans must move their civilization to some place more secure. Employing anti-gravity generators, the Inhumans moved their entire city and its foundation in one piece. The new site of Attilan, a hidden valley in the Himalayan Mountain range in China, was excavated by the Eternals, another variant offshoot of humanity. The Himalayan site of Attilan became known as "the Great Refuge." The Himalayas did not prove to be remote enough to enable the Inhumans to retain their secrecy, however, and soon the Inhumans' existence became known to several of the governments of the outside world, although not to the general public. While in the Himalayas, all of Attilan's ancient architecture was accidentally destroyed by Black Bolt and the city has been extensively redesigned and rebuilt.
Since Earth air is deadly to the Inhumans when Attilan was on Earth it had protective barriers. It had five separate defensive systems. A trillion-volt palisade, a progressive eco-filter to scrub the rancid air. And a dome of impenetrable negative space surrounding it all. Attilan was relocated once again, this time to escape the effects of Earthly pollution and disease. Attilan is currently located in the Blue Area of the Moon, nestled in the ruins of an ancient city built by the alien Kree whose technology gives the Blue Area its own artificially created atmosphere.
Attilan defenses are very powerful. It has been able to travel outside of Earth in space without being damaged. It has also been able to take an attack of cannons and bombs. Th e shield would evaporate the bombs and just absorb the energy, making it stronger on every attack. There was a machine that Maximus built that would disrupt the shield and cause it to fall. With this and lightning the shield of Attilan would fall. Even though the shield is very strong it has been compromised by the Kree and the Skrulls.
Outside of Attilan is a junkyard of Shi'ar technology that the Inhumans do not use. This space is used as a playground for curious Inhuman children. Underneath the city of Attilan lies the Alpha Primitives, and the technology that keeps Attilan working. This is a basement like structure full of machines that the Alpha Primitives call mother.
After the Inhumans took over leadership of the Kree Empire, Attilan was moved to Hala, the capital of the empire. Once the Inhumans returned to earth they floated in space for a while until moving to off the coast of Manhattan.
During the events of Infinity Thanos sends Corvus to Attilan with the demands of a tribute of Inhumans between the ages of sixteen to twenty two or else all Inhumans will be slaughtered. Black Bolt knows the true reasons for Thanos coming to Earth and orders Maximus to evacuate everyone off Attilan. Maximus then proceeds to arm the terrigen bomb. When Thanos arrives on Attilian and demands Black Bolt to tell him the location of his son. Black Bolt responds by unleashing a sonic scream which triggers the terrigen bomb to go off destroying the Attilan.
Attilan is far more technologically advanced than other cities of its era. The Inhumans have used their technology to relocate the city and the island upon which it is built to other locations, even taking it off of the planet itself.
Attilan appears as a base in the video-game Marvel: Ultimate Alliance when the heroes are saved from Doom by the Watcher.
Marvel Cinematic Universe
Attilan is revealed to be the symbols Agent Coulson is sketching on the wall in season 2 of Marvel's Agents of S.H.I.E.L.D., the sketches when laid out three dimensionally turn out to be the architecture of the city. Coulson states that a force was drawing him to the city, but once he discovered what it was no longer feels the urge to go there.