Outlander Gaelic Marching Song from 209 Je Suis Prest, also used with magnificent effect in Season 5, episode 1 “The Fiery Cross”, see the video just below to hear composer, Bear McCreary’s commentary on including this piece.
The haunting song a Jacobite anthem which accompanied Jamie, Claire and the men who marched towards their destiny is called
Moch sa mhadainn ’s mi dùsgadh (also called Oran Eile Don Phrionnsa – Song to the Prince).
Artist: Griogair Labhruidh
Here is the song for your listening pleasure.
From Season 5.
Would you follow Jamie into battle?
Here is the translation.