Sacred Icon Suite 2
From Halopedia, the Halo wiki
Sacred Icon Suite 2 is a song from the Halo Legends: Original Soundtrack. It is a partial arrangement of the Sacred Icon Suite from the Halo 2: Original Soundtrack. It plays near during the episode Origins, in the scene depicting allied Human and Covenant forces fighting the Flood. This track was also used in the announcement trailer for the Defiant Map Pack DLC for Halo: Reach, as well as in the Halo Channel PAX Prime trailer.
The first part of the song consists of a heavily orchestrated version of Weight of Failure/(the final two minutes of) Destroyer's Invocation/Cortege (the Arbiter's motif) from the Sacred Icon Suite. The second part is a fully orchestrated and lively arrangement of Unforgotten/Never Forget, where a choir takes over the main melody, reinforced by a full orchestral arrangement, bringing the piece to its climax. The final few seconds feature the melody of Opening Volley.