"Sumer is icumen in" is Old English, is it not? Certainly not pre-Roman invasion, in that form, but who knows what its antecedents were?The oldest-rooted one I happen to be aware of is "Lord Randal, My Son", which I understand goes WAY back, and through MANY countries.
And how about the golden-ball songs, whose descendant I know as "Slack your rope, hangs-a-man". I've been told that goes WAY back, and widespread too.
Dave Oesterreich