Hidden messages

Hidden messages can be found in the games Halo 2 and Halo 3. These were inserted into music tracks and reversed to mask their meanings.

Black Tower
In this message, "sunlight" refers to a new dawn, while "broken column" to destruction. Based on this, it can be deduced that the Gravemind is referring to the extinction of the Forerunner. "Other kingdom"; this would mean, refers to the current Galaxy. "Prayers to broken stone" suggests that he plans on destroying the Covenant, or perhaps all sentient races.

Gravemind
This message is played in the Halo 3 track "Gravemind", which is played near to the end of "The Covenant". The message relates to Gravemind's plans on galactic conquest, starting first with the collapse of Earth via an en-mass assault. The second sentence refers to his intentions after ending his temporary alliance as the total destruction of the Fleet of Retribution and its allied Human warships, along with their crews.

Mausoleum Suite
This message is unusual in the sense that it does not appear to be the Gravemind's word. Instead, they seem to be 032 Mendicant Bias' words. Mendicant Bias seeks "forgiveness for [his] horrible crimes". As his actions led to the destruction of his fleet and his dismantling, he "[lives] in a prison of [his] own demise". Likewise, being the creation of a race extinct for 100,000 years, he is also "lost in time".