Part of the process of awakening the Mother is chanting Mantras. There are eight Mantras to chant (one for each area) in the ruins; once all eight are chanted, the final Ankh in the True Shrine of the Mother will be surrounded by the 4 seals you must break to activate it.
Required items
Wedge
"Drive the wedges through the rear."
--Giltorriyo.
The Wedge is located by a pyramid in the Tower of Ruin. In order to access this area, you must defeat Palenque to open a number 6 door in the Chamber of Birth, which leads into a passage in the Chamber of Extinction that connects to another passage in the Inferno Cavern. You also must defeat Baphomet, whose defeat unlocks the number 7 door in the Cavern. The door leads into the pyramid area.
Once at the pyramid, climb down to a room with a pedestal. Trigger it, climb back up, and head left to a room where you must battle Nu Wa. Defeat it to open the chest within the room; it contains the Wedge.
Magatama Jewel
No, you can't break Psyche-Locks with this thing.
Defeat Tiamat in the Dimensional Corridor to get the Magatama Jewel.
Mantra location tablets
By now, the sphinx in the Temple of the Sun (F-3) should have crumbled.
Go past where it is located into a secret room containing eight tablets. Each of these tablets, save for the center one, cryptically describes the location of each mantra tablet.
Mantra locations and chanting
To chant a mantra, you need to locate a differently-shaped tablet and read it. You must also have chanted every mantra before it or else the mantra tablet will not show up (i.e. you can't chant the Twin Labyrinths mantra unless you've chanted the one in the Endless Corridor).
Then, locate a compass (marked red on Ruins RAM 16K/24K), and the boss room. Take note of where the boss room in the frontside is in relation to the compass. Then, go to the backside equivalent of the area you are in (unless you are already in the backside), locate the compass, and go to the room where the boss would be in relation to the compass. There, type in the name to chant and a seal marked with the number of the area should appear.
Note: If you type too fast, the game may not register your typing. Make sure the previous key is released before typing the next one. Although the mantra is in all caps, you cannot have the shift key held down while typing it. You cannot save and reload until done chanting all mantras else you will have to start at the first one.
"In a corridor"
The first mantra is in a corridor. The entrance to the corridor that continues forever.*Tablet location: Endless Corridor (D-1) Chant the name. The one who Tiamat loved and hated. The source of the pain who gave birth to the 11 monsters. MARDUK.*Where to chant: Endless Corridor (C-1)
"Feet of the twins"
The second Mantra is by the feet of the twins. The place where their feet connect.*Tablet location: Twin Labyrinths (E-5) Chant the name. That of the witches' banquet for Baphomet. The name of the place where summoned demons return. SABBAT.*Where to chant: Twin Labyrinths (I-5)
"Green Beast"
The third Mantra is a green beast. By the side of the guardian of Hell.*Tablet location: Chamber of Extinction (D-1) Chant the name. That of the Nameless One. The name of the Nameless One who travels to the sky. MU.*Where to chant: Chamber of Birth (B-4)
"Serpent"
The fourth Mantra is by a serpent. The path connecting to the pyramid Nu Wa guards.*Tablet location: Inferno Cavern (B-1 to F-2) Chant the name. That of the ugly demon that lives deep within the earth. The name of the one with the drooping eyelid. VIY.*Where to chant: Tower of Ruin (C-4)
"Feet of the Goddess"
The fifth Mantra is below the goddess. By the feet of the goddess who gazes at the crumbing tower.*Tablet location: Tower of the Goddess (B-8) Chant the name. The name of the distant rough ocean. The dark waves under which Bahamut lives. BAHRUN.*Where to chant: Tower of the Goddess (D-4)
"The Eye"
No hint tablet.*Tablet location: Temple of the Sun (C-3) Chant the name. That of the eye that watches the truth. The name of the one who watches over and gives blessings to all. UDJAT.*Where to chant: Temple of Moonlight (D-6)
"Many spikes"
The seventh Mantra is by many spikes. Spikes that protrude from seven floors.*Tablet location: Graveyard of the Giants (F-3) Chant the name. That of the one who records the sorrow of the Giants. He who weeps over the death of his people. ABT.*Where to chant: Graveyard of the Giants (D-4)
"Eight stars"
The final Mantra is eight stars.*Tablet location: Guidance Gate (B-6) Chant the name. That of the beginning of everything. And give her an eternal rest as the final child. LAMULANA.*Where to chant: Confusion Gate (C-3)