Black Tower
From Halopedia, the Halo wiki
Black Tower is a song included in the Halo 3: Original Soundtrack. It plays during the level The Covenant, and is the second movement of the Covenant Suite. Also, when you play it in reverse, you can hear a message from Gravemind. This is related to T.S. Elliots' poem, The Hollow Men.
The message in this song says:
"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." The quote is from The Hollow Men by T.S. Eliot.
It runs for 6 minutes and 3.702 seconds (6:03.702).
The second half of the piece, "Heroes Also Fall", is a remake of the "Rue and Woe" movement of High Charity Suite, and is appropriately played during Miranda Keyes' death scene.
