A seal that held back the evil of the First Faceless One. It was discovered, later, that it did not hold him, but his armies, led by Tloke, giving it it's name. All soldiers in the vicinity were killed, including Marshal Dorleone, who broke the seal. A few soldiers escaped but were eventually killed within two weeks.
An account of the seal is found in the account Cave Horror which was recorded by Explorer's League agents looking for survivors. Cave Survivor's disappearance likely means that there are no more survivors.
Tloke then used the forces of darkness that were sealed there to destroy the army of Sabbatholm, which was still retreating after the Battle of Sorrow's Refuge. He then turned his eye to the Arcadian Army.
Taken from the Explorer's League documents.
'The background shows a big circle,with many circles in it. Dragon like drawings are at the four points. “Yes. Circles within circles. Dragons were carved into the wall and those same walls were painted pitch black. Yet...” '
'At the center of the circles within circles was a gauntlet.'
The document describes the words as some kind of Elvish: 'Remove the gauntlet and release the great evil of the First Faceless one' as the inscription.
'As we turned around, he saw the other gauntlet, sister to the seal'
When released, the seal sent out hands that grasped Dorleone and dragged him into darkness.