Seventh Level
From Tolkien Gateway
The Seventh Level of Moria or Khazad-dûm was its highest level of chambers, corridors and rooms, being six levels above the Great Gates. The term level or levels in the ancient Dwarven kingdom generally refer to the eastern area of Moria, nearest the eastern gate which was most populated when Khazad-dûm was a mighty city of the Dwarves.
The Chamber of Mazarbul was located on the Seventh Level of Moria.
