"I'm not forcing you to come with me. If you can cross the Mire with its sinking-mud and poisonous blow-holes--not to mention the muglumps, oozefish and white ravens that would rip you apart as soon as look at you...Well, it's your choice."
The Mire was the open stretch of land between Undertown and the Twilight Woods. During the First and Second Ages of Flight it was hostile, toxic, and covered in bleached white mud from centuries of Undertown's waste being dumped there. During the Third Age of Flight it changed into a grassy plains full of many species of birds. However, dangerous poisonous blow-holes were still active.
In the First Age of Flight
For most of the First Age of Flight the Mire was dangerous to cross and mostly uninhabited. The only permanent inhabitants were the guides, usually bleached white like the mud around them and often treacherous, who led travellers across the Mire for exorbitant prices. However, near the end of the First Age of Flight the Great Mire Road was built and a settlement, the Armada of the Dead, was established in the Mire.
In the Second Age of Flight
By the time of the Second Age of Flight the Mire had become easy to cross due to the Great Mire Road, although it was not entirely risk free; the shrykes controlled it. All trade to and from Undertown passed through the Mire along the road. The sky pirates, who had realised that stone-sickness was picking them off one by one, scuttled all their ships together and formed the Armada of the Dead in the Mire. The sky pirates of the armada were led by Deadbolt Vulpoon and raided the Great Mire Road to survive. Both the road and the armada were destroyed by the Dark Maelstrom, and the Third Great Migration, which was triggered by the Dark Maelstrom, passed through the Mire.
In the Third Age of Flight
During the Third Age of Flight the Mire was entirely abandoned. There were no permanent residents in the Mire and the only known trips that passed by it were the two voyages of the Archemax and the journeys of the various gloamglozer-led migrant groups.
Role in the Edge Chronicles
In the Twig Trilogy
During Stormchaser the survivors of the disastrous stormchasing mission had to cross the Mire to get back to Undertown. Their guide was Screed Toe-Taker, but he betrayed them. Screed cut of Hubble's toes after he succumbed to his wounds, murdered Spiker, and tried to kill the Stone Pilot. Twig stopped Screed and fought him, managing to kill him due to a timely shout of “Screedius Tollinix” from the Professor of Light that distracted Screed. The Professor died shortly after from his wounds. Then Twig and the Stone Pilot repaired Screed’s old ship, the Windcutter, and flew out of the Mire and back to Undertown with his stash of stormphrax.
In the Rook Trilogy
During The Last of the Sky Pirates, Rook, Magda, and Stob crossed the Mire on the Great Mire Road. Along the way Rook talked to the imprisoned Deadbolt Vulpoon and witnessed the raid that freed him. In Freeglader the participants of the Third Great Migration crossed the Mire.