In
Lord of the Rings there are citations of “living” used in this same sense as the “living stone” of the
Noldor’s stairs along the coastlands south of Drengist. (p 159 in the book
The Fall of Gondolin) Describing his battle against
Durin’s Bane,
Gandalf recalled, “We fought far under the
living earth,” and the Endless Stair which “issued at last in Durin’s Tower carved in the
living rock of Zirak-zigil.” (
Two Towers, “White Rider”)
Also in
Two Towers, “Road to
Isengard”, narration describes the gates of Isengard as “so wrought and poised upon their huge hinges, posts of steel driven into the
living stone, that when unbarred they could be moved with a light thrust of the arms.”
Return of the King, “Mount Doom”, narration describing
the One Ring after
Gollum bit off
Frodo’s finger, which was still thrust through
the Ring: “It shone now as if verily it was wrought of
living fire.”
We have here four examples: “living earth”, “living rock”, “living stone”, “living fire”. I suppose the last, “living fire”, is easiest:
frozen fire might be its opposite, but “living fire” indicates something burning. The phrase “living stone” appears in
The Fall of Gondolin and is also the subject of Rivendell_librarian’s question: in this case, I think it means the steel posts of the
Númenórean gates of Isengard were driven into the rock of the wall, which was (the phrase indicates, I think) a naturally occurring structure the Dúnedain shaped and used to their own purposes, namely to enclose the circle of
Angrenost and the tower of
Orthanc. The example “living rock” is nearly identical: Durin’s Tower was carved and shaped from the natural pinnacle of stone atop the
Silvertine. In which case “living earth” means the natural formations beneath the earth, unshaped by the
Balrog, the
Dwarves, and possibly (probably) even the Nameless Things that gnawed the “living earth” at that great depth.
In short, “living stone” is neither unique to
Fall of Gondolin nor a peculiar turn of phrase – for
Tolkien, that is.
As for the steel gate, the seventh, last, and strongest of the Seven Gates of
Gondolin, I tip my hat to Squint-eyed Southerner: perhaps they were made of
mithril. But if they were of steel, we should recall that they were constructed by Maeglin before his capture and treason, when he was still loyal to his uncle,
Turgon the King, meant to be the most beautiful, the mightiest, and most impressive of the Seven Gates: for when
Tuor stepped through, he could see the
city rising from Tumladen. The first six gates were already in place, and gold was used last: Maeglin needed something stronger, something resistant, something
shiny, and steel is strong, resistant, and shiny: after all, it is in place for a martial purpose.