The Corries, "Loch Lomond". One of the great folksongs of all time. Sung often, it has many versions, but this is the one that matters. The first published version was in 1841, but it is almost certainly a fair amount earlier than that. It refers to the Jacobite Rising of the Forty-Five.
O well may I weep
for yest're'en in my sleep,
we stood bride and bridegroom together.
But his arms and his breath
were as cold as the death
And his heart's blood ran red in the heather.
As for the chorus, which is the most famous part because it is so striking, nobody has anything but speculation about what 'the high road' and 'the low road' are supposed to mean.