Also, note the Green Emphasis:

Unifying Opposites to reach Solution.......

Many years ago, the powerful Sartan ended a war by sundering the world into four elemental worlds, and imprisoned their enemies, the Patryns, in     

>>>   a labyrinth that became demonic.  <<<

[The Parasitic Factor Comes Into Being

The Labyrinth Becomes A Kill Zone / Torture Chamber]

Shortly afterwards, the Sartan mysteriously disappeared. Centuries later, the first Patryns escaped the Labyrinth, and have just learned how to access the other worlds. The books follow the fiercely independent Haplo, a Patryn agent sent to scout the four worlds in preparation for conquest by his master.

Before the books

The Earth was destroyed.
Four worlds were created out of the ruin. Worlds for ourselves and the mensch: Air, Fire, Stone, Water.

Four Gates connect each world to the other: Arianus to Pryan to Abarrach to Chelestra.

A house of correction was built for our enemies: the Labyrinth.
The Labyrinth is connected to the other worlds through the Fifth Gate: the Nexus.

The Sixth Gate is the center, permitting entry: the Vortex.

And all was accomplished through the Seventh Gate.
The end was the beginning.

Eventually the Sartan, led by Samah and his Council of Seven, undertook drastic measures to win, and broke the planet Earth into four separate worlds, each one focusing on a separate element (air, earth, fire, and water). This cataclysmic moment of destruction and re-creation is known as the Sundering. Millions of mensch died, with only chosen populations magically isolated for resettlement. How the Patryns were saved is not known, though surviving Sartan have spoken of the ease with which they once captured the nomadic, isolated Patryns in the days before the Sundering. The Sartan also created the Labyrinth, where they imprisoned the Patryns for rehabilitation. In the center of it was the Vortex, where the Patryns were initially placed along with Sartan who had disagreed with the Sundering, and where the mensch were temporarily housed during the Sundering itself. The Labyrinth was surrounded by the Nexus, a paradise city for the Patryns to live in once they had become civilized; the Nexus, the Labyrinth, and the Vortex are arranged in concentric circles. All of these worlds are connected by Death's Gate, and smaller, one-way gates allow each elemental world to feed the other worlds whatever they lack.

The Sartan were left in stewardship of not just one world, but many, all designed to work in perfect harmony. Almost immediately, however, things began to go wrong. Strange serpents that the Sartan had not created appeared on Chelestra.

Samah, fearing what would happen if the serpents spread to the other worlds, felt forced to shut Death's Gate; the Sartan then placed themselves into a stasis sleep, expecting it to only last long enough for the other worlds to finish their parts of the grand plan. On Arianus, the Sartan also slumbered, in the hopes that their world would improve.

[In the meantime, the mensch lost all knowledge of their past; the lost Sartan of Arianus and Pryan became mythical god figures to the dwarves and elves of those worlds, respectively. This left the imprisoned Patryns as the only ones who still remembered some of their heritage.

Haplo and Alfred have only one door to jump through: Death's Gate itself, which is slowly collapsing and taking all of creation with it. Haplo and Alfred have to combine forces, forcing their magics to work together–Patryn and Sartan rune-structures, diametric opposites... That fit together so obviously, Haplo wonders why it has never been seen before. Their spell works, and with a dull thud, Death's Gate closes for the final time.