Music by Kevin MacLeod. Available under the Creative Commons Attribution 3.0 Unported license. Download link: https://incompetech.com/music/royalty-free/index.html?isrc=USUAN1100880

MacLeod's description:

Genre: Soundtrack
Length: 3:34
Instruments: Strings, French Horn, Trombones, Percussion, Flute
Tempo: 110

A piece in three or four parts... depending on how you count parts. The penultimate section features a lonely flute, slowly joined by a children's choir, and finally exploding into a giant choral and orchestral ending.
From the original soundtrack to "The Last Stand of the Mechanolith".
ISRC: US-UAN-11-00880
Epic, Intense, Somber 2011