Reversed messages refer to a series of messages hidden in Halo music tracks. There are thirteen reversed messages in the Halo series: one in Halo 2, three in Halo 3, 8 in Halo: Reach, and one in Halo 2: Anniversary.

Destroyer's Invocation Message

In the Halo 2 soundtrack Destroyer's Invocation, (the first movement of the Mausoleum Suite on the Halo 2: Original Soundtrack), a mysterious voice chants. If this mumbling is reversed (listen), a voice is heard saying:

...I have walked among men and angels for three thousand years. Time has no end... no beginning... no purpose.
I wander the earth, seeking forgiveness for my horrible crimes against God and man.
I live to see death and destruction, evil... over the light, but the light cannot be extinguished.
I live in a prison of my own demise.'
I am lost...in time

The voice can be heard in the beginning cutscene of the level The Arbiter, the level Gravemind when John-117 rescues the Marines, and during the level The Great Journey when Thel 'Vadam battles Tartarus.

In 2007, Martin O'Donnell posted on the halo.bungie.org forums that he wondered "why the transcript (of the reversed message) is still wrong."[1]

Black Tower Message

In the Halo 3 soundtrack, during the first few minutes of the track Black Tower, there is yet another message that can be heard if one reverses the music. Here is a transcript:

Eyes from Death's dream kingdom,
Appear as sunlight on a broken column.
There in Death's other kingdom walking alone,
Trembling lips form prayers to broken stone.

This message appears to be a reference to T.S. Elliot's Poem, The Hollow Men. The first part of the transcript refers to lines 20-23.

In death’s dream kingdom
These do not appear:
There, the eyes are
Sunlight on a broken column

The second part refers to lines 47-49.

Waking alone
At the hour when we are
Trembling with tenderness
Lips that would kiss
Form prayers to broken stone.

It is also worth noting that lines from the last stanza in T.S. Elliot's The Hollow Men were used in the Cortana Letters, which was repeated at end of the Halo 3 Announcement trailer and in Halo 3 itself.

Dread Intrusion Message

In the Halo 3 soundtrack, a reversed message can be heard in the tracks Gravemind, and Dread Intrusion. The entire message is currently unknown, however, several lines are intelligible. Oddly, the voice during these messages sounds different from Gravemind. It echoes considerably, rendering several lines unknown, it is much deeper in pitch, and multiple other voices can be heard. This could be a reference to multiple Graveminds from the past that speak as one because of inherited knowledge. The first two lines both have 7 syllables each, a possible 7 reference.

Side by side, we march as one,
Humans and Elites will die,
The Earth will fall if we strike together,
So forth shall all of life.

The exact person who is speaking is unknown. Just like the Destroyer's Invocation Message, there are many possibilities about who it could be. The likely candidates are the Gravemind and the Prophet of Truth, since only Elites and humans are mentioned.

A voice can also be heard on the level, The Covenant. It can be found on the second barrier tower's control room, where there are Brute Stalkers.

Data Pads

Similar to the Halo 3's Terminals, Halo: Reach has reversed Forerunner audio in the background of the Data pads.[2]

Culling data
Corruption contained
Breach identified
Welcome Scion
Lineage confirmed
Rogue confirmed
Purge Initiated
Protocols Reinstated
Gathering sources
Scouring Arrays
Prioritizing
Cross-referencing
Referencing
Daemon Running
Searching
Researching

Cryptic Whisper Message

In the Halo 2: Anniversary soundtrack Cryptic Whisper a mysterious voice chants. If this mumbling is reversed, a voice is heard saying:

We squander eons in the darkness
While they seize our triumphs for their own
The Mantle of Responsibility for all things belongs to Forerunners alone
Think of my acts as you will
Do not doubt the reality
The Reclamation has already begun
We are hopeless to stop it.

The voice can be heard in the beginning cutscene of the level The Arbiter. The message alludes to the Ur-Didact's suasoria from Halo 4's Epilogue.

Sources