The Seven Seals

The Seven Seals are seven structures that the Gods put in place when they constructed the Material plane. Contained within each is power enough to reshape large portions of the plane to the whim of whomever breaks it. This power comes with a cost: a great sacrifice on the level of a mighty god must be made. The beings soul is consumed by the seal and removed from existence entirely.

The First Seal - Irrgaten (The Underdark, the Great Caves, Labirinto)
The first seal was the underdark.

Asmodeus sacrificed Dis and Avernus along with all inhabiting them to break the first seal. With it, he turned the caverns into a landing ground and fortress for the devils invading the material plane. It's breaking caused a massive earthquake on the surface, and Irrgaten's restructuring altered the above ground forever.

The Second Seal - Vier Graben (The Pillars, The Four Trenches, Colonne di Mare)
The second seal was 4 great trenches held open by 4 great pillars at the bottom of the sea.

Asmodeus sacrificed Stygia and Cania along with all those inhabiting them to break the second seal. With it, he turned the four great currents of the sea into great diseases that spread across the land, air, and sea. It's breaking caused plagues and poisoned waters across the surface.

The Third Seal - Mondschlussel (The Moon, The Mother, Cielo Chiave)
The third seal was the moon.

Asmodeus sacrificed Phlegethos and Minauros and all those inhabiting them to break the third seal. The seal was painted red with the blood of those who were consumed by it and the seal shattered in the sky. With it, he released the great horrors that were locked away in the skies and rained them down onto the earth.

The Fourth Seal - Berg Sinai (Mount Sinai, The Peak, Gabal Musa)
The fourth seal was the great mountain to the south of Tubberham.

The Rawgoh family of Tubberham and the Siebensiegels of Iry Shem sacrificed the 4 Angels of Tubberham to break the fourth seal. With its breaking, Mount Sinai cracked in twain and became the greater and lesser peaks of Horeb. Its breaking reversed one of The Calamities.

The Fifth Seal - Schlussel un Abgrund (The Key & The Abyss, Hell's Mouth, Porta Inferno)
The fifth seal was a great trench dividing the Tormented Land of Gug and the Unctuous Sea of Magog.

The Siebensiegels of Iry Shem sacrificed the supernatural armies of Wormwood of Gug and Chernabog of Magog to break the fifth seal. Its breaking opened a portal to the surface of the river sticks within a giant maw where a great ravine one stood. With its breaking one of The Calamities was reversed.

The Sixth Seal - Der Fluss (The Great Dam of Malbolge, The Flood, L'alluvione)
The sixth seal was a great dam built in hell to prevent the River Styx's water from destroying the plane.

The Siebensiegels of Iry Shem sacrificed the Iron City, Mephistopheles, Malbolge, Malodomini, and all those inhabiting to break the sixth seal. Its breaking tore down the dam on the River Styx and flooded Hell with its water. With its breaking one of The Calamities was reversed.

The Seventh Seal - Ofen Herz (Nessus, The Heart of the Furnace, Cuore Della Furnace)
The seventh seal was the H|Prison of Malsheem to hold the evil being Asmodeus. A giant labyrinthine dungeon whose furnace held Asmodeus and his chains.

The Siebensiegels of Iry Shem sacrificed Asmodeus and his prison to break the seventh seal. Its breaking was contested by Asmodeus attempting to sacrifice the Siebensiegels and rule over two planes and conquer the multiverse. Its breaking required Asmodeus to be chained to the furnace and the flames to be doused. With its breaking, all of Hell was destroyed and all its minions were eliminated from the material plane forever.