So I been doing some guitar fingerpicking of hymns, one of which is a plainchant that sounds awesome. I started looking at the earliest Christian hymns known to see what else is out there and learned of Ordo Virtutum, by Hildegard of Bingen, from about 1511. It's more of a concert than a song and I found a awesome video of it being performed with English subtitles:
Ordo Virtutum - Circle of Virtue - The Song Company
Ordo Virtutum - Circle of Virtue - The Song Company