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human
[Lord Of The Rings] What is exactly The Dead Marshes? Who are those people?
gpt
The marshes predate the Battle of Dagorlad, but at the time it was an open plain. That's why they call it it Dagorlad, from Sindarin *dagor* (battle) and *lad* (plain). The marsh crept in after the clash of arms.

The Last Alliance of Men and Elves led by the human King Elendil (father to the doomed Isildur) and the elvish King Gil-Galad were marching on Mordor, and had just linked up with the Numenorian host under Elendil’s other son Anarion. Together, they marched from the strongholds of Osgiliath and Minas Ithil (the same tower that would one day be known by the dread name of Minas Morgul) against the Black Gate to the north.

They were blitzed by a sallying force of literally millions of Orcs, fallen and corrupted men, and other evil creatures that skulk about without names. The Last Alliance hadn't expected a counter attack, figuring that the forces of Sauron would stay safe behind their walls.

The Battle of Dagorlad fought on the open plain near the marsh was apocalyptic. A large detachment of Wood Elves from Greenwood charged prematurely and without orders, and got bogged down by the legions of orcs. Unsupported as they were, the Wood Elves were slaughtered, with two out of every three elves dying. King Oropher of Greenwood fell valiantly, leaving his son Thranduil (Legolas' dad) to take the shattered remnants of the Wood Elf army back home to Mirthwood, vowing to never commit to a southern war again.

Elendil, Anarion, and Gil-Galad pushed forward, committed to the battle against their will by Oropher's foolhardy charge. They prevailed; the forces of Mordor were wiped out almost to a man. The bodies of the millions of elves, orcs, and men had to be left where they fell; the coming siege of the Black Gate and the planned march on Barad-dur would brook no delays, and they had suffered 50% casualties and so could spare no diggers to boot.

Over time, the marshes near the open plain spread and submerged the corpses in the murk and the muck. Now, they are the Dead Marshes. The bodies may or may not be actually present, time and decay being what they are, but the spirits of the restless dead float along nonetheless.