Third Deep

Within old Khazad-dûm, there were many levels running upwards and downwards within the Mountains of Moria. Those floors that lay below the level of the Great Gates on the eastern side of the mountains were known as Deeps, and were numbered counting downward. So, on entering Khazad-dûm through the East-gate, and after passing through the First Hall, one would come to a wide flight of steps that led downward toward the Second Hall in the First Deep. A level below that lay the Second Deep and, below that, the Third Deep.

We have few details of what was to be found on each of these Deeps, but we do have one brief reference to the Third Deep, recorded during the time that Balin briefly held Moria. In the Book of Mazarbul, it is said that one of his companions, Óin, went to seek the upper armouries, and that these were to be found on the Third Deep. This would place the armouries two levels down from the Second Hall and the Bridge of Khazad-dûm. We are not told whether Óin succeeded in his mission, but the fact that these were the 'upper' armouries implies that there were more armouries (and doubtless many other chambers besides) to be found on lower Deeps cut farther down into the earth.