Slag-hills

A region on the outer edge of the Desolation of the Morannon, the blasted and lifeless region before the Gates of Mordor. This was a broken land of pits and mounds, with craters and pools filled with ash and slime. The Slag-hills from which it took its name were conical piles of broken stone, arranged in rows across the landscape, leaking choking fumes from their hidden interiors.

The Slag-hills were encountered by Frodo, Sam and Gollum as they made their way towards the Morannon. They briefly hid behind one of the hills, but were soon driven off by the foul vapours it emitted. Twenty-one days later, Aragorn and the Captains of the West led their Host into the same region, and it was here that they were surrounded by the forces of Mordor in the moments before Sauron's downfall.

The nature, purposes and origins of the Slag-hills are almost entirely mysterious. 'Slag' usually refers to waste stone, and there is indeed a reference to the hills as being the 'vomit of the maggot-folk of Mordor',² so perhaps the mounds were simply rubble from the tunnelling of the Orcs of Mordor (we know that the Maggot-folk had numerous tunnels in the mountains of this region).

If the hills were simply heaps of waste stone, that does not help to explain why they were systematically arranged '...like an obscene graveyard in endless rows'.³ Nor does it explain why these piles of rock would emit foul vapours into the surrounding landscape. Perhaps they were intended as a part of Mordor's defences, though if so, they seem to have had very little obvious effect.

As noted above, the word 'slag' usually refers to stone waste, and that does seem to be the intended meaning here, but the word can occasionally have a secondary meaning, as a reference to rock blasted out of a volcano. Given the presence of Mount Doom within Mordor, this alternative meaning might possibly be relevant. On this reading, Sauron would have had to send his servants on a journey of eighty miles or more, from Orodruin out through the Morannon, to create ordered rows of mounds in the wasteland beyond. Indeed, the desolate landscape is described as a '...monument to the dark labour of [Mordor's] slaves...' (ibid), so this is not impossible, though it is difficult to fathom what purpose it might have served.