Marathon: Istoria Soundtrack

The soundtrack was created by Jonathan G. Irons (irons) and contains 22 tracks. It is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License (http://creativecommons.org/licenses/by-sa/4.0/).

Listen on YouTube.

Internet Archive upload:
https://archive.org/details/istoria-soundtrack

If you really like it, you can buy it on Bandcamp. The Bandcamp release contains high-quality versions of the files (48k/24-bit FLAC, for example). It also includes liner notes:
https://music.jonirons.net/album/istoria