Black Tower is a song included in the Halo 3: Original Soundtrack. It contains the tracks Black Tower and Heroes Also Fall. 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.
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.