Agartha

is a hidden civilization of a near-human species callehans that live in caves deep under the surface of the Earth.

For ages, legends have recounted the advanced technologies of these underground dwellers in various cultures around the woren living on the Atlantis continent.

It is believed that Agartha is roughly 300 miles underground, in the zone between the upper and lower mantles. Agartha consists of dozens of cities full of massive superstructures built into constantly-winding rocky caverns and fed by underground rivers, lakes and even oceans. There are many cave routes from the surface to Agartha, most are hidden and known only to the Agarthans.

It is unknown what the current population is of these people, but it is estimated to be more than 500,000 but less than 3,000,000.

Agartha goes by many names. It is also called the Underworld, or the Core. The term "Men from within the Earth" is an American intelligence designation for the Agarthan race.

Despite possessing highly advanced technology, as a whole the Agarthan race has been regressing for the past two thousand years. As a result, much of their civilization has become run-down and in a constant state of repair with very little new technologies or discoveries being made.

Going Underground
According to Zerrath, up until 10,000 years ago (roughly 8000 BCE) the race that became the Agarthans had ruled the Earth and it's inhabitants from their continent of Atlantis. But their then-leader Zalanubar was experimenting on what was then known as the Sapphire of Power. In his attempts to weaponize the Sapphire itself, he inadvertently caused it to explode, releasing a massive amount of energy into the atmosphere. This caused a chain reaction that resulted in a worldwide calamity, eventually destroying the continent of Atantis.

The survivors fled into underground sanctuaries. As time wore on and their numbers grew, they moved deeper and deeper into the Earth and came up to the surface far less frequently. Eventually they closed up their civilization and hid away from life on the surface, seeing the emerging human civilizations as a threat to their own existence.

Known Agarthans
Not much is known about the methods in which the Men from within the Earth live, but a few details have stood out. There is an Agarthan High Command which consists of a leader and several underlings who have been identified:

Master Zun - Supreme Leader of the Men from within the Earth.

Zorak - Supreme Commander and Second-in-Command. Heir apparent to Master Zun.

Zerrath - War Minister and Third-in-Command.

Zagim - Undercover Agarthan agent who somehow infiltrated the FBI as Assistant Director Smith, later exposed and killed by FBI Agent Cooper.

Zerg - Agarthan commander of a small team sent to the surface to recover the missing Sapphire of Agartha, stolen by undercover FBI Agent Nicholson, later killed by FBI Agent Cooper.

Zella - Trusted agent of Master Zun and member of his Assassin Corps, she came to the surface to assist Zerg and later Zerrath with recovering the Sapphire of Agartha

Zong - A scout and saboteur who patrolled both the Tibet and Blue Ridge Mountains entrances to the Underworld, later killed by Operative-132 and FBI Agent Cooper.

Known Entrances to Agartha
The following list is of confirmed tunnels that eventually lead down to the civilization of Agartha: Additionally, it has been suggested that there are other, as-yet-undiscovered entrances in North America, Europe, Asia, Africa, South America, Australia, and Antarctica.
 * Himalayan Mountains, Tibet. Used by Zong, as seen in Diabolical Tales: Part I.
 * The Gorge, near the Blue Ridge Mountains, Maryland USA. Used by Zong, Zerg, Zerrath and others, as seen in Diabolical Tales: Part I, Part II, and Part III. 
 * Superstition Mountains, Arizona USA. Used by Agent Nicholson and Zellor, as seen in Diabolical Tales: Part II. 
 * Lituya Mountain, Alaska, USA. Mentioned by Operative-132 in Diabolical Tales: Part II. 

Appearances
Agartha has not actually been seen, only referred to.
 * Diabolical Tales: Part I - Genesis of the Men From Within The Earth (mentioned only)
 * Diabolical Tales: Part II - Vengeance of the Men From Within The Earth (mentioned only)
 * Diabolical Tales: Part III - Betrayal of the Men From Within The Earth (mentioned only)
 * Diabolical Tales: The Enigma Files (mentioned only)

Behind the Scenes
Agartha is the name of a legendary underground city near the center of the Earth. It operates on the many "Hollow Earth" theories especially prevalent in late 19th Century science-fiction.

Rumors of an entrance to this underworld empire, sometimes also called "Shangri-La", that exists in the Himalayan Mountains of Tibet have been told for generations.