Orhan marble (Liaboan marble) was a special kind of rock with powers of repelling dark souls, associated with the moon of the light gods for its heavenly quality. It was not actually a mineral originating on the Great Moon, but rather a rare form of limestone that would work as a magical talisman with sufficient purity. In its purest form it was bluish-white and would glow bright blue in the presence of creatures or servants of the Unlife. The repulsion effect would be an attack that had to be resisted somewhere below level 10, and it would ward off undead which were level 3 or lower.
While the phrase itself is not necessarily used, its properties have been manifest within the game. It may be an implicit aspect of the warding mechanism on the gate of the Order of Voln, which cannot be passed by Council of Light masters, and in the past there was a room in The Graveyard that the undead would not enter unless repelled into it by a Cleric. Its purpose in this case was symbolic.
Behind the Scenes
Prior to a change in the roaming mechanics for creatures around roughly the year 2000, monsters avoided the (impure) marble obelisk where Kestrel Etrevion's sons were buried. The green marble may reflect the idea that at least one of them worshipped the serpent god, which is supported by the ruined cult in the underground stronghold of the Coastal Cliffs. It might also be an allusion to the lizard god monolith in "The Doom That Came to Sarnath", along with the stone of the crypt being brought from marvelous distances, which is a story referenced underground in the Purgatory segment.
[Graveyard] Several graves here are clustered around a large marble monument. A low iron railing encloses the area. The burial plots seem to be unplundered, but the dark, freshly turned earth atop one of the graves indicates the presence of an unquiet soul. You also see a faded path. Obvious paths: west >look monument The green-veined marble monument is a plain obelisk, tall and thin, with no ornamental carving. There is an engraving on the wide base. >read base In the Common language, it reads: Here lie the sons of Kestrel Etrevion, princes all, who perished in the battle to regain their ancestral land.
Ancient Egyptian obelisks were intended to serve as magical wardings to guard the dead, as well as act as conduits for the soul to travel to the sun god who resided within it. The sun god would be Klysus (Luukos), consistent with his I.C.E. Age lore, with the incorporation of Orhan marble being blasphemous both to him and Eissa (Lorminstra). However, his role as a sun god in the Lankan Empire may not have been established yet when The Graveyard was written, which would simply reduce his symbolic role to the serpent and soul devourer in the sun god mythology. The sun is still relevant from the Egyptian motifs and the role of Hell as where "the sun in silence rests." The relationship between Klysus and Lorgalis was well-established in the lore when The Graveyard was designed.
The sun is also important because Eissa is the sister of the god of night (and dreams) who crusades against the Unlife, and Bandur's goddesses Kadaena and Orgiana (Eorgina) are associated with flames. (Indeed, his inordinate focus on goddesses is suggestive within the Osiris/Set and Isis mythology, especially since Orgiana was an expressly male-hating deity. "The Legend of the Necropolis of Etrevion" insinuates this jealousy of Kestrel.) Since the surface of The Graveyard represents Oblivion, the obelisk points toward the River of Life and so the light, whereas "the dark path" descends into the Void. Without ornamental carvings there was no guidance toward the afterlife. The symbolism is that the nephews were doomed to limbo forever, beyond the reach of either death god.